johannes ennings

Electronic Submission Identification Number : xxxxx

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Technological Evolution

at the Producer–Consumer Interface Draft 2 (January 5, 2000)

JOHANNES M. PENNINGS

The Wharton School

University of Pennsylvania 2000 Steinberg Hall – Dietrich Hall

Philadelphia, PA 19104 – 6370

phone (215) 898 – 7755 fax (215) 898 – 0401

[email protected]

and

HANN OHL KIM

Australian Graduate School of Management University of New South Wales

Sydney 2052 Australia

phone +61 – 2 – 9931 – 9552

fax +61 – 2 – 9313 – 7279 [email protected]

Electronic Submission Identification Number : 12140

Submitted to Technology and Innovation Management Division,

Academy of Management Meetings Toronto

2000


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ABSTRACT

This paper examines the emergence of dominant designs in the tennis racket industry.

Unlike other studies, we consider both the competitive dynamics among firms

comprising the industry, as well as the choice behavior of consumers. We assume that

innovations are usually surrounded by a good deal of causal ambiguity, giving producers

opportunities for shaping consumer choice behavior, but on the other hand according a

greater weight to visible and legitimate actors on the demand side who can alleviate

ambiguity about new products. In short, we very much stress the need to jointly consider

both supply and demand conditions and to view producers and consumers in interaction

with each other. Furthermore, we hold the selection environment in which new and

existing designs come and go, to include both economic (e.g., number of competitors)

and institutional (e.g., regulation) factors.

We distinguish several dominant designs, based on material head, width and

length of racket. Some designs are superior than other ones, based on physical and

consumer ratings, but quality is ambiguous, and even so, better designs do not always

win.

The main thrust of the paper revolves around the degree of professional endorsement of

new racket designs which is associated with the likelihood replication by competitors.

While controlling for other variables, this relationship is indeed empirical. Obtaining

data from trade publications, consumer magazines, and laboratory tests, we examined the

effects of environmental, firm and product characteristics. The window of observation

was 1975-1999, but some variables were missing for some time intervals. Using a

generalized maximum likelihood estimation procedure, the findings suggest that next to

endorsement, advertising and product quality are prominent in accounting for the success

and failure of new product introductions. The implication is that we should not only

focus on firm attributes, its strategy or size of market, but we should also discover what

consumers want and how firms can satisfy their needs with a good product.

Keywords: dominant design, technological trajectory, consumers, tennis racket.


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Technological Evolution at the Producer–Consumer Interface

I. INTRODUCTION

Technological evolutions or “technological trajectories” (Dosi, 1982) are usually

attributed to competitive conditions among industry incumbents and new entrants.

Schumpeter (1934) was among the first to have spelled out the conditions that undermine

the status quo in an industry, the improvement or demise of a dominant design and its

replacement by a new one. Dominant designs get exchanged as innovative investments

produce new components and/or new architectures.

In this paper, we explore the emergence of dominant designs in the tennis racket

industry. However, unlike other studies, we consider not only the conduct of

competitors, but include also the choice behavior of consumers. While firms can certainly

change or solidify consumer preferences regarding new products and services, we should

consider those preferences in their own right. We highlight the importance of consumer

preferences in accounting for successful product innovations.

In the following paragraphs, we develop a framework for innovation that centers

on the producer-consumer interface. First, we consider a concern with that interface,

rather than with the more conventional, exclusive focus on producers for understanding

the dominant design emergence. The views surrounding producers’ role in shaping

technological evolutions have been well documented. Next, we explore some aspects

that figure prominently in the interface, most notably advertising as input for legitimizing

innovations by producers and consumers, and examine that interface as a selection

environment that comprises both market and institutional conditions. The results support


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our hypothesis that consumer preference management is critical in technological

evolution.

II. A PRODUCER–CONSUMER INTERFACE FRAMEWORK

Whether in traditional industrial economics (Sutton, 1991) or economic history

(Sahal, 1981), it is widely assumed that the dominant position in the industry is an

inevitable consequence of technical efficiency of an ex post successful alternative.

However, technological change towards superiority is not self-evident as technical

efficiency considerations constitute only one of the factors that shape a technology break-

through (e.g., David, 1985; Arthur, 1989; Podolny and Stuart, 1995; Anderson and

Tushman, 1990). A new technology might have multiple, but uncorrelated benefits, or a

mixture of positive and negative outcomes (e.g., Hoch and Ha, 1986). However, research

is typically slanted towards the emergence of new dominant designs, with the benefit (or

drawback!) of hindsight, and little knowledge exists about efforts at establishing new

designs that faltered.

II. 1. Producers

The role of firms in shaping technological trajectories is well documented. The

definition of the market, and the competitive interdependencies among its firms are the

central focus of industrial economics. Markets typically are viewed as firms supplying

goods and services that are close substitutes and thus have high cross-elasticities

(Robinson, 1933). Market boundaries derive from the gaps in demand such that products

within the same market have higher cross elasticities of demand than products belonging

to different markets. The market might be segregated cross-sectionally or inter-

temporally. When innovations produce new products having diminished cross elasticities


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with obsolete ones, we observe the emergence of a new market, or convergence from

existing ones, e.g., the video game industry and consumer owned communication

technologies, or TVs and PCs (Greenstein and Khanna, 1997).

It has been suggested that the early and late stages of an industry resemble the

‘entrepreneurial’ and ‘routinized’ regimes, respectively (e.g., Utterback, 1995). This

qualitative shift in technological regimes occurs with the emergence of a dominant

design. When the industry standard has been firmly established, incumbent firms are in a

better position to command a lion’s share of the market because their capabilities in

process innovation confer competitive advantages over entrants. The impact of dominant

designs has been documented in various industries such as typewriter, automobile,

television, and transistor (Utterback and Suarez, 1993).

Many innovations are introduced by new entrants. However, when incumbents

posseses complementary assets, i.e., the specialized supporting resources necessary for

successful commercialization of an innovation, they have competitive advantage over

new entrants introducing an innovation (Teece, 1986). Tripsas (1997) indicates that

incumbents in the typesetting industry, endowed with certain complementary assets (such

as a proprietary font library), might overcome the death of a dominant design to which

they were wedded. These firms redeployed those assets during the arrival of a new

design by attaching them to new architectures. In the tennis racket industry, firms

introducing new designs may be at an advantages as they are already endowed with

complementary assets such as marketing and distribution capabilities.

This “producer” literature thus dwells on the relationship between the nature of

innovation, firm characteristics, and industry dynamics. Not much attention is given to


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the process by which certain innovations come to be widely adopted by competitors and

potential users.

The diffusion process plays an important role in technological evolution. It is rare

for an innovator to solely satisfy the aggregate market demand. Furthermore, the

evolutionary path of technological development significantly changes depending on the

extent to which an innovation is imitated by competitors: the decline of Macintosh in

personal computing is an oft-cited example. Therefore, the process of imitation or

diffusion is the mechanism by which new technologies come to acquire economic

significance. According to Nelson and Winter (1982), few studies formally treat the

imitation stage as part of a more general theory of technological change. Technological

diffusion is a process that spreads successful varieties of products and processes through

an economic structure and displaces wholly or partly the existing varieties (Rogers,

1995). Early diffusion studies attempted to find empirical regularities (e.g., Grilliches,

1957; Mansfield, 1961) as illustrated by the well-known S-shaped curve.

II. 2. Consumers

The role of consumers is generally not considered when tracking and accounting

for the emergence, divergence or convergence of technologies. Markets are defined by

the set of producers whose products have high cross-elasticities. The role of consumers at

the end of the value chain and their interaction with upstream firms is disregarded,

although the original meaning of markets goes back to the Middle Ages when buyers and

sellers congregated in the town market, a well bounded physical locale. This imagery is

also prevalent among sociologists (e.g., White, 1981) who define markets as self-

reproducing structures of roles (of buyers and sellers). Today, markets are mostly abstract


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and inferred from demand and supply structures. To give adequate status to consumers,

we need to move away from the exclusive focus of firms in shaping those demand/supply

structures. Consumer choice behavior should not be treated as a given. Rather, we could

focus on the buyer-supplier relationships, and view a market as an ongoing network that

evolves around a product or service. Several ingredients for a framework suggest

themselves now. As the term implies, innovation involves novelty and, therefore,

embodies uncertainty. We begin with a review of choice models accommodating

uncertainty. Then we examine related issues including advertising and the selection

environment for new products and services, which bifurcates into “market” and

“institutional” selection environments. Under conditions of uncertainty and limited

rationality, the “clearing” of a product by the market gets complemented by non-market

selection processes.

Behavioral Decision Theory

Unlike classical economists, we cannot assume that consumers are rational--rather

their rationality is bounded due to their limited computational capabilities. Following the

early writings by Simon (e.g., 1955), March (1978) has elaborated on rational decision

making. He gives a qualified endorsement to rational choice models due to the absence of

a clearly defined preference structure: “Human beings have unstable, inconsistent,

incompletely evoked, and imprecise goals at least in part because human abilities limit

preference orderliness” (March, 1978: 598). One reason for these “ambiguous tastes” is

that their limited cognitive capability affects information processing about future

preferences of consequences of current actions just as it affects information processing

about “future consequences of current actions” as Simon (1955) emphasized. Human


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beings (and institutions) “intelligently choose to have ambiguous tastes” (March, 1978:

598) partly because they recognize that our tastes are constructed and interpreted through

various experiences. Along this line, he argues that human beings view “inconsistency as

a normal, and necessary, aspect of the development and clarification of tastes” (March,

1978: 599). Compared with established products and the habit formation that has taken

its course, new products provoke a higher level of search and greater intensity of choice

behavior.

The combination of bounded rationality (Simon, 1955; March, 1978) and novelty

of innovative products poses a challenging task to consumers. First, consumers

experience difficulties in getting relevant information on the overall quality of new

products or the benefit of new product features. In many cases, we observe a lack of

consensus over whether a particular innovation improves the performance of the product

and who stands to benefit. In the absence of accurate information about new products we

should not assume that consumers can make rational choices as stipulated in traditional

economic models (Simon, 1955).

Another challenge surfaces around the capacity of new products in meeting

specific needs. Innovations typically add new features to existing products. Innovations,

by definition, introduce products that are new to the market. When innovations are

incremental, consumers deal with a relatively simple problem of comparing cost and

benefit. However, when more radical or discontinuous, we cannot assume the existence

of a well-defined preference structure for judging the presence or absence of an

innovation’s benefits. Since such novel products are foreign to the market, it is unlikely

that consumers possess already well developed preference structures. Consumer


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evaluation of new products then inevitably accompanies guesses regarding their future

preferences. Innovation produces two classes of uncertainty, uncertainty about quality

and uncertainty about preferences (Ellsberg (1961). Such uncertainty requires us to view

the acceptance of a new product through a lens that encompasses also non-market

attributes.

Ambiguity, Innovation, and Advertising

As innovations entail ambiguity, and firms are deemed quite influential in shaping

cognitions regarding a novel product’s features, it is of considerable interest to explore

how firms set the tone in a producer-consumer interface. Facing new features and

dimensions of the new product, consumers cannot depend on their prior knowledge

structure for the product and consumption patterns: they rather need to modify previous

cognitive schemas or develop a new set of preferences. During the early stages of a

product’s life cycle, the causal ambiguity awaits diminution, while at the end of the

cycle, consumers have acquired the requisite cognitive categories for evaluating a

product’s features. Product quality evaluation under ambiguity can be more appropriately

represented as a learning process than as a choice problem: consumer evaluation of new

features is a learning process through which they update their knowledge about the nature

of the product (Veryzer, 1998). The process through which consumers assess product

quality is posited as “an intuitive hypothesis-testing process whereby one of the most

important sources for tentative hypotheses is advertising (Hoch and Ha, 1986). While

economists treat advertising as a source of information (Nelson, 1970, 1974;

Schmalensee, 1978), consumers often do not seem to believe what is claimed in

advertising because they recognize the possibility that firms have incentives to lie about


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their products. Recent studies in marketing rather treat advertising as a source for

tentative hypotheses (Hoch and Ha, 1986). Consumers take an eclectic approach to

advertising because they use advertising as a source of new information but at the same

time they are skeptical about its validity. So temporary hypotheses emerge in consumers’

minds by advertising and consumers wait to either believe or discard it until they have a

chance to test the product themselves. When confirmed, they accept but when

disconfirmed by experience, they reject the hypotheses.

Then, the next question is how consumers interpret the information from

experience with specific hypotheses in their mind. Human information processing can

take a form of either concept-driven or data-driven (Bobrow and Norman, 1975; Gavetti

and Levinthal, 2000). The former, also called on-line or top-down information

processing, denotes the pattern by which prior expectations and knowledge guide which

information will be selected and how it will be interpreted. That is, people do not pay

equal attention to all information. Rather they put more weight on the information that is

consistent with their prior expectations and beliefs. The information is interpreted as

consistent with their hypothetical relationship.

In contrast, people sometimes adopt the opposite, the data-driven, bottom-up

information processing. In this case, prior expectations do not play a critical role.

Individuals update and revise their prior beliefs based on new information by interpreting

the information at its “face” value: prior expectations do not “interfere” with the

supposedly correct message of the information.

The above argument opens up the possibility of firm intervention into consumer

product evaluation of new products. Since innovations often break the established


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perception of the product and its function, they challenge the quality and usefulness of

old versus new products and unravel the extant preferences for making a commensurate

evaluation. Therefore, the management of consumer perception of innovations is critical

for their success. Schumpeter stressed the active role of the entrepreneurial firm by

arguing that “changes in consumers’ tastes are brought about by the action of producers”

(Schumpeter, 1939: 73). Then, the question is “how.” As discussed above, one way that

the firm can actively form a working hypothesis about its innovations in consumer’s

mind is advertising.

The tennis racket industry appears to be highly typical for such a setting. We can

explore that market vis-a-vis other markets, say the market for squash rackets or golf

clubs, but we might also focus on successive markets where product and process

innovations trigger discontinuous markets over time (e.g., Utterback and Abernathy,

1975), say, the market for wooden rackets versus the market for aluminum rackets. As we

will see, the tennis racket industry shows successive dominant designs that became the

industry standard, but also numerous designs that never reached a minimal critical mass

to merit such a status. Nor should we assume that the selection environment in a market

like that of tennis rackets consists largely of the market’s invisible hand, as we often also

detect the presence of visible hands, most notably governmental, legal, regulatory and

other institutional forces.

II. 3. Market versus Institutional Selection Forces

For analytical purposes we might distinguish between market and institutional

forces as comprising a novel product’s selection environment. It is plausible to argue

that a product’s causal ambiguity might give comparatively more weight to institutional


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forces. We find evidence for such pronouncements in complex and simple technologies

that vie for the dominant design--as illustrated by NTSC and Qwerty standards

respectively. For example, the Qwerty keyboard might be ergonomically awkward, but

unlikely to entangle some of the characters’ hammers and thus not slow down the typing

task. The NTSC television standard became the US standard because RCA was well

connected with the Federal Communication Commission, a regulatory agency that could

more readily be manipulated by RCA and not by RCA’s competitors which lacked

RCA’s social capital (Collis, Bane and Bradley, 1997). The NTSC adoption was not

exclusively predicated on its picture video quality as any international traveler can attest.

Summarizing, when causal ambiguity prevails, producers might signal superiority,

thus shaping the technological evolution, for example through advertising, demonstration

projects and other modes of signaling. Producers enjoy considerable leverage in

manipulating the debate around products, especially ambiguous ones. Many markets are

socially constructed and reproduced. This follows not only from the above statement that

markets and their products comprise self-regulating systems of roles that are observable

at the producer-consumer interface. Social construction is most salient when we

encounter high levels of uncertainty, and unequivocal reference points are lacking.

III. THE TENNIS RACKET INDUSTRY

The sporting goods industry in general, and the tennis racket industry in

particular, provides an attractive opportunity for studying technological innovation.

While some sporting goods have been immune to change – most notably the baseball bat

and the field hockey stick, others have shown dramatic changes – golf clubs and tennis

rackets among them the most visible ones. The study of the tennis racket should lend


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itself to an examination of evolving dominant designs and is very suitable to deal with

the above issues.

The tennis racket is a relatively simple product with a rather uncomplicated

architecture and transparent product components. Its technological development is easily

discernible with several distinct changes that permit a rather unambiguous punctuation in

developmental stages. The development into different stages also supports improvement

in product qualities, although as we will see, such improvements are shrouded by

uncertainty. Apparently, those improvements have not always produced superior

performance among athletes, using the new artifacts. Thus, there remains ambiguity

regarding product improvements.

Ironically, the institutional context has also produced considerable resistance to

innovation and has been reluctant to embrace new product designs, however evident or

erroneous the product enhancements seem to be. New equipment might enable players to

generate more power with equivalent amounts of force expended, reduce variability in

accuracy with the same skill level, and reduce various safety concerns without tampering

with the sport’s integrity. Or it might trigger compassionate debates about the veracity of

product improvement enhancement, the advertising claims by presumably deceitful firms,

and the bribing of influential opinion leaders. In any event, the greater than 1000 product

introductions and a correspondingly large number of patents granted, renders a

comparison with fruit flies appropriate: this setting provides large numbers of relatively

simple observations, and, therefore, is ideal for examining supply and demand conditions

that destroy and embellish successive dominant designs.

III. 1. The Tennis Racket’s Evolution


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The tennis racket has quite a long and rich history. While the oldest racket-shape

instrument documented in the literature goes back to the 16th century, it is rather similar

to the modern racquetball instrument in that it is about seven to ten inches long. The

modern tennis racket, which established the oval face and 68 cm (27-inch)-long frame

standard, was developed in 1873. Despite the long history, significant technological

discontinuities began to take place since 1967 when the first metal tennis racket was

introduced. Figure 1 illustrates the concentration of innovative activities in the past three

decades. The number of patents issued by the U.S. Patent and Trademark Office in the

class 273/73(Amusement Devices: Games/name) and D21/212 (Games, Toys, and

Sporting Goods/name) steeply increased in the early 1970s. The number of patents

containing keywords "tennis racket" or "tennis racquet" also shows a similar pattern.

[ Insert Figure 1 about here ]

Improvements in materials and its processing technology have played a

significant role in the advancement of racket development. New materials such as steel,

aluminum, fiberglass, graphite, boron, and titanium gradually replaced wood because the

former is stiffer and more durable than the latter. Interesting developments also took

place in racket design, and some of them were possible due to advanced materials.

Among others, three innovations stand out.

The first is the oversize racket in 1976 developed by Prince, a ball machine

company at the time. It has the face of 784 cm2 (110 square inches) compared to the 460

cm2 (70 square inch) face of the traditional racket. While it might appear trivial, the

over-size idea is regarded as the most revolutionary in the industry's history because it

broke the mind of designers free from the tradition. The second is the wide-body racket


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of Wilson in 1987. Its frame has a 39mm-thick cross section beam at the thickest part,

while the traditional racket has a constant beam of only 19mm. The last is the extra-

length racket, which ranges from 71cm (28 inches) to 81cm (32 inches). The length of

the racket had remained at 68cm (27 inches) since the late 19th century until the first

commercially successful 71cm (28-inch) racket was introduced in 1995. These three

design innovations along with the development in materials have produced a series of

changes in dominant designs in the industry (Figure 2).


In addition to these three dominant technologies, numerous new technologies

have been introduced that achieved only moderate success. Pro Kennex developed a

racket that has about 100 micro vials in the racket frame which adds extra momentum to

the ball and reduces the transmission of racket shock and vibration (Ashley, 1993). A

number of companies have developed rackets with a string pattern other than the

traditional two-way horizontal/perpendicular string pattern. A two-way diagonal by

Victor Sports and Völkl, and a three-way string pattern by MadRaq are notable. These

rackets are claimed to enlarge the sweet spot. Snauwaert, BioSports, and Sentra

developed ergonomically designed rackets that place the sweet spot differently and

reduce stress on the wrist of players. Figure 3 illustrates a few of those unusual

innovations.


III. 2. Ambiguity

The success of an innovation – its imitation by competitors and its acceptance by

consumers – is implicitly regarded as an inevitable consequence of its technical


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superiority. It is widely assumed that consumers as well as producers are capable of

perceiving benefits of an innovation, and technological evolution follows its own logic.

However, economic agents of both sides of the market experience a significant amount

of uncertainty and ambiguity when new technologies and products are introduced to the

market.

There are two types of ambiguity that render the detection of an innovation

benefit tenuous. The first results from the fact that the benefit of an innovation is often

not evident. For example, Ellsberg (1961) claimed that innovations pose a challenging

task to decision-makers due to the lack of relevant information. Presumably, experts are

better equipped to form appropriate judgments, yet the heuristics they employ preclude

the suspension of decision biases (Kahneman and Tversky, 1979). While the oversize

racket is now unanimously praised as the most important innovation in the history of the

tennis racket industry, it faced resistance even from industry experts. In a review article,

an industry expert intimated by commenting that,

“After playing the Prince racket for a while, I must admit that I was a bit disappointed. The racket showed very little torsional rigidity, excessive vibration on off-center hits, and a marked tendency to "spoon" or bend at the head of the racket. Innovation in any sport is healthy, but I feel the Prince is more of a gimmick, not a true step forward in high performance racket technology. It is best used by beginners or novices.” (From Fiott, 1978: 66, italics added)

Our expert regards the benefit of an oversize racket as a simple psychological advantage.

However, it turned out that an oversize racket has a definitive advantage over a

traditional size racket because the former enlarges the sweet spot on the racket (Brody,

1979).


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The story behind a recent ITF (International Tennis Federation) ruling of banning

the racket longer than 74cm (29 inches) also illustrates the ambiguity and uncertainty

caused by an innovation. The ITF, the rule-governing body of tennis, changed the

maximum length of the racket from 81cm (32 inches) to 74cm (29 inches) because it felt

that high speed, powerful serves produced by extra-length rackets would diminish the

popularity of tennis as a spectator as well as a participant sport. However, an experiment

conducted by Tennis magazine shows that the real benefit of extra lengths comes from a

higher accuracy rather than increased power and speed (Table 2).

[ Insert Table 2 about here ]

The second type of ambiguity results from a poor or moderate correlation

between product attributes. A low correlation generates considerable discretion for

consumers and induces uncertainty about optimum choices (Hoch and Ha, 1986). In the

case of tennis rackets, three product attributes – stiffness, stability, and power – are

employed as representative characteristics. Table 3 provides the correlations between the

three attributes measured by instruments and a panel of players. It shows that the three

attributes have only moderate to low correlations. Furthermore, a low inter-subject

correlation indicates that it is difficult for players to agree on the characteristics of a

particular racket.


III. 3. Producer-Consumer Interface through Professional Endorsement

When ambiguity prevails, the sense making activity becomes critical in

determining the path of technological development. It has been widely documented that

individuals tend to stay with a current option when the benefit of a new alternative is not


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clear (Kahneman and Tversky, 1979; Thaler, 1980). Samuelson and Zeckhauser (1988)

show that people weigh potential losses from switching from the product to a new one

larger than the same amount of potential gains from a new product: they call it the "status

quo" bias. This phenomenon creates a barrier that entrepreneurs should overcome

through various activities. According to Schumpeter,

“...the great majority of changes in commodities consumed has been forced by producers on consumers who, more often than not, have resisted the change and have had to be educated up by elaborate psychotechnics of advertising.” (From Schumpeter, 1939: 73)

This Schumpeterean observation point has an important implication in the present

argument. Given the uncorrelated relationship among performance attributes, the

superiority of any tennis racket is equivocal. When its benefits are elusive, consumers

are reluctant to switch. This tendency is reinforced due to the conservatism in the tennis

community. An innovator's commercialization efforts take on extra significance. While

development of technically superior products is important, it is the beginning of the

entrepreneurial process rather than its end.

Racket manufacturers resort to professional tennis players in providing a strong

message to consumers about their products. Having top players use the product, as they

are highly visible and respected in the tennis community, can increase the legitimacy of a

new product. Also, the confusion regarding the performance of the racket can be

significantly reduced when high status individuals perform well with a new racket.

When the first oversize racket was introduced, it was criticized by industry experts as a

gimmick (Fiott, 1978). However, negative responses against the racket subsided when

Pam Shriver, a female professional player, surprised the tennis community by advancing

to the final of the U.S. Open in 1978 playing with the Prince oversize racket. Her success


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with a new design signaled innovation benefits about this racket because she had never

reached even the quarterfinals of women's singles championships in any Grand Slam

event before. She provided pseudo-proof that the oversize racket is not just for

"beginners or novices" (Fiott, 1978: 66) who need extra help from the equipment but

rather enhances the performance level for players at any level (Le Marche, 1986).

In short, by making professional players use their product, innovators affect the

acceptance of a new technology because professional players' endorsement provides

familiarity and legitimacy (Veryzer, 1998; Ohanian, 1991). Even in the absence of

induced usage, when players voluntarily pick their own design, the legitimization of that

design might resolve ambiguity, and thus produce a trigger toward ramp-up in its

diffusion. The following quote is from an industry expert who accords with our

argument:

“...but if the past is any guide, successful racket design concepts will emerge from the ranks of tennis players and enthusiasts. "Familiarity seems to lead to conformity in this business," Leonard said.” (From Ashley, 1993: 55)

Based on these arguments, we propose the following hypothesis:

Hypothesis The top professional tennis players’ endorsement of the racket with a focal racket design is positively associated with the likelihood of replication of the design, after controlling the effects of other variables.

Our concern with demand side conditions does not rule out the endogenous

aspects of producers in shaping the rise and fall of dominant designs. We might consider

the conventional factors, including the size of the firm (as a proxy for tangible resource

endowments), R&D intensity, and intangible assets that are complementary with any


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new product introduction. We should also heed the importance of institutional conditions,

most notably the role of regulation in legitimizing certain innovations.

IV. METHOD

IV. 1. Empirical Models

Available data allow us to test the above hypothesis and are expected to help in

resolving the central issue of the paper: we need to consider both producer and consumer

aspects since consumers matter too in the rise and fall of dominant designs. To explore

the hypothesis, Poisson regression was first considered. While Poisson regression is

widely considered as the base model for the analysis of count data, adjustments are often

required because assumptions of the model are not always satisfied. In particular, when

the assumption that the mean and the variance are equal (E(y) = Var(y) = λ) is violated,

the following problems arise even if the coefficients are not biased (Allison, 1999):

underestimation of the standard errors, overestimation of the chi-square statistics, and

inefficiency of the maximum likelihood estimation. The phenomenon is often referred to

overdispersion. In this study, the variance (0.243) exceeds the mean (0.06) so that we

need to make the necessary adjustments. The overdispersion problem is amended by

including a gamma-distributed error term in the equation (Cameron and Trivedi, 1986;

Hausman, Hall, and Griliches, 1984):

log λi = β0 + β1χi1 + β2χi2 + …+ βkχik + σεi. [1]

Here, the dependent variable Yi is assumed to have a Poisson distribution with expected

value λi, conditional on εi, and the unconditional distribution of yi has a negative

binomial distribution (Allison, 1999).


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While the negative binomial takes into account the overdispersion problem, it

does not address the correlation among observations (Barron, 1992). In this study, each

year has multiple observations depending on the racket design considered. For example,

the year of 1990 appears in the dataset multiple times for the counts of new rackets with

oversize design, widebody design, and longbody design, to just name a few. Since some

of the variables such as the market and institutional characteristics are correlated among

these observations in the same year, the correlation should be accounted for in the

estimation. Due to the assumption of independence among observations, the maximum

likelihood estimation is not appropriate for this study. Instead, we employ the method of

generalized estimating equations (GEE, hereafter) which addresses the correlation among

observations (Allison, 1999; Diggle, Liang, and Zeger, 1994). In the maximum

likelihood estimation, the iteratively reweighted least squares algorithm is used where

observations are treated statistically independent. It means that a weight matrix W has

off-diagonal elements equal to 0 and diagonal elements equal to pi(1 – pi), where pi is the

predicted probability from the previous iteration. In the GEE procedure, however, off-

diagonal elements of the matrix W are allowed to have non-zero values, which are

functions of the correlations among the observations. The GEE estimation can be

obtained by SAS 6.12 through the so called GENMOD procedure with REPEATED

statement (Allison, 1999).

The model employed to analyze adoption of new design had the general

specification of the following:

Yi (t) = αi (t) + β1Χi,1(t – 1) + β2Χi,2 + β3Χi,3 (t – 1) + σεI [2]


22

where Yi refers to the number of rackets adopting new design, and Χ1, Χ2, and

Χ3, are vectors of variables, description of which follows below.

Χ1 denotes a vector of variables representing the environmental conditions at time

(t – 1). First, we include the size of the tennis playing population because it determines

the carrying capacity of the environment. Second, the number of firms in the market, the

number of rackets in the market, and their square terms are included. Furthermore, major

regulatory changes are included as dummy variables since it is well documented that they

have crucial impacts on the nature of innovative activities (Garud and Rappa, 1994). In

the tennis racket industry, the International Tennis Federation’s ruling on equipments

such as rackets and balls is the major legal barrier for new innovations. Therefore, we

create dummy variables for the years of 1980 and 1997 in which ITF made major

changes in the section 4 (Rackets) in Rules of Tennis.

X2 is a matrix of variables representing the characteristics of the innovating firm.

Previous studies in economics and sociology have primarily focused on the

characteristics of the firm that is more (less) likely to innovate. In order to see whether

the firm’s effort to actively persuade consumers to favor its innovation is robust even

after we take the firm characteristics into consideration, we include the following in the

model: (1) whether the innovating firm is a new entrant or an incumbent firm, (2)

whether the firm has other related businesses, and (3) whether the firm is a U.S. or a

foreign entity.

X3 includes the number of top professional players who endorse and use a tennis

racket with a new technology of interest, the quality index of the racket with a technology

of interest, the amount of advertising in popular magazines, and their interaction terms.


23

As we discussed above, when a top professional player uses a racket with a new

technology, she not only helps consumers form a tentative hypothesis regarding the

benefit of the new technology, but also enhances its legitimacy. However, it can be

argued that a new technology is replicated due to its technical superiority. In order to

rule out this argument, we include a measure of the quality of a tennis racket with an

innovative technology.

IV. 2. Data

Information on the introduction of new tennis rackets is available from popular

magazines such as World Tennis and Tennis. Two reasons make them an attractive

source of information. First, manufacturers run advertisements when they introduce new

tennis rackets that contain detailed information about unique features of the racket.

Second, the magazines have sections in which experts review the racket currently

available in the market. From various issues of these magazines, we identified 1,292 new

tennis rackets during the period between 1965 and 1995.

The Sporting Goods Directory published by the Sporting Goods Dealers

Association contains the name of the company and its products. This information

enables us to construct variables on firm characteristics such as age and environmental

characteristics like the number of firms. Dummy variables for regulatory changes were

constructed by referring to various issues of Rules of Tennis published by the

International Tennis Federation. The market size is measured by the tennis playing

population and collected from the publication by Sports Business Research Network.


24

IV. 3. Measurement of the Variables

Table 1 provides the description of the variables used in this study. In the

following paragraphs we will first describe the dependent variable followed by the

independent variables. The independent variables include attributes of the market, the

manufacturers, the product design and the product. A very important category involves

the quality of the racket.

Dependent Variable

In our hypothesis, the dependent variable was racket design adoption by

competing firms. Therefore, every single new tennis racket introduced to the U.S. market

was the subject of our study. The question was whether the racket embodied a certain

racket design. The measurement of racket design adoption was straightforward because

the specification of new rackets was readily available in various sources. The dependent

variable was coded 1 when the racket embodied focal racket design and 0 otherwise.1

Eight racket designs were considered in the analysis: (1) oversized head, (2) extra length,

(3) tension adjust device, (4) ergonomic design, (5) three directional string design, (6)

convex throat design, (7) fan string pattern, and (8) widebody design.2

Independent Variables

Professional Endorsement Whether a new racket was used by top professional players

was derived from various issues in popular tennis magazines such as World Tennis,

Tennis, and Tennis Industry. We define top professional players as those who were

included in the top 10 players of the year list published by the Association of Tennis

Professionals (ATP) for male players and the Women’s Tennis Association (WTA) for

female players, respectively. In addition to the top 10 players both in men’s and


25

women’s annual rankings, we also included those players who reached semi-finals at four

Grand Slam tournaments (Wimbledon, U.S. Open, French Open, and Australian Open)

because they attract a significant amount of attention from the tennis community even

though they were not top ten players. This is legitimate because the ranking of players is

only a proxy for those players who are highly visible in the tennis community.

Advertising As a proxy for advertising spending, we counted the number of advertising

pages in Tennis. We collected the information from August and December issues of the

magazine each year. Those issues were chosen because it was expected for racket

manufacturers to concentrate their promotion efforts in these two months: August issues

run the U.S. Open special coverage and December issues include an annual review of the

industry. When a full one page advertisement was dedicated for one tennis racket, we

counted it as 1. When a multiple number of rackets appeared in a one page

advertisement, we gave each racket (1/the number of rackets on the page). When a

manufacturer ran a two page advertisement for one racket, we counted two for the racket.

By the same token, 0.5 was given to the case in which an advertisement only occupied a

half page. When racket design adoption was the main concern, we summed the number

of advertising pages promoting a specific racket design. For example, not only Prince,

the original innovator of the oversize racket, but also followers promoted their oversize

rackets in advertising. Since the advertising by followers contributed to the increase in

familiarity and acceptability of the oversize design, we collapsed each manufacturer’s

advertising count into one for the overall oversize design. We noticed that the amount of

advertising varied across years. In order to control this variation, we divided the count of

advertising for each racket and design by the total number of advertising pages per year.


26

Design Quality Quality of racket design poses a critical and challenging task to this

study. It would be ideal if the underlying technological merit of individual racket design

could be objectively measured regardless of its application. However, such information

is not available. Instead, we collected data on performance of rackets, rather than

designs, from a series of racket reviews published in World Tennis. It is believed that

this measure could be used as a substitute for individual design quality because the

contribution of a particular design to racket quality should be reflected on overall racket

quality. If a design truly improves playing characteristics of the racket, overall quality of

the rackets with the focal design should be higher than that of those without the focal

design. Therefore, we compared quality of the racket with focal design to that of rackets

without it, and used this relative measure of racket quality as a quality measure of the

racket design.

World Tennis published a series of articles on racket quality based on extensive

tests over fifteen years. The tests consisted of two very different parts: one measured by

scientific instruments in the lab and the other measured by players on the tennis court.

The lab test was conducted by three scientists at MIT. They measured three dimensions

of the tennis racket that are believed to critically influence its quality.3 The numbers

reported in the magazine were the average numbers given by multiple testers, who vary

in gender and playing style. In addition to the three dimensions, the item called

“playability” measured overall quality of the racket.

While these quality measures were used for individual rackets when individual

racket sales were concerned, we constructed the following variable when new design

adoption was of interest. When the success of racket design is an issue, what matters is


27

how good a racket with focal design could be in comparison to quality of rackets without

the design. In other words, since what we need to measure is the frontier that could be

achieved with a particular racket design, we chose the racket with the highest quality

index from a group of rackets with focal design as the number representing racket design

quality that could be accomplished at the time. Furthermore, we standardized the quality

index with the mean and variance of quality of rackets without focal design. Therefore,

best quality index for racket design i was calculated as the following:4

).(.

)(

2~,

2~,,,

−≠

−≠−=

ttij

ttijtiti QualityDevStd

QualityAverageyBestQualityIndexBestQualit [3]

where j=1, 2,…, i, …, k racket designs.

The results reported in the following are based on the comparison with the rackets

without focal design introduced in the past two years from the year of interest since three

years, rather than one, is considered reasonable as a window of competition rather than

one year.5

V. RESULTS

Table 4 reports the results on new racket introduction data during the period from

1981 to 1992. The effects of environmental characteristics and innovator characteristics

on the dependent variable were first estimated (Models 1 and 2). Of particular interest is

whether the innovator is a new entrant: a new racket design developed by an incumbent

firm is more likely to be replicated.


In addition to the variables included in Models 1 and 2, we added design related

variables (Models 3 and 4). First, when interaction was not considered (Model 3), only


28

professional endorsement had positive effects on the design replication: neither design

quality nor advertising was significant. However, when an interaction term was included

(Model 4), all three main effect variables, i.e., professional endorsement, design quality,

and advertising, turned out to be significant. In addition, the interaction between

professional endorsement and design quality was also significant. The interaction

between professional endorsement and advertising was not reported in Model 4 since it

was not significant and did not change the effect of any other variable.

VI. IMPLICATION

This study has an implication for the selection environment within evolutionary

perspectives. Facing the anomalies of an arguably inferior technology’s dominance in

the market (e.g, David, 1985), researchers have attempted to uncover the selection

environment, which has been largely treated as a black box. While some attribute the

seemingly contradictory outcome to “historically small events” (Arthur, 1989) in the

presence of positive feedback effects, others emphasize more systematic issues such as

the role of the institutional environment (e.g., Garud and Rappa, 1994).

These studies, however, keep silent on one of the key elements of the selection

environment: consumers. Recent studies begin to recognize the importance of consumers

as a critical component of the selection environment and attempt to bring demand side

issues into discussion. Cowan, Cowan, and Swann (1997) argue that the market as we

know it properly functions only when consumption as well as production side evolve

together. What really separates these studies from traditional approaches is that

consumers are not assumed to have fixed preferences. They lament on the assumption of

exogenously given preference which has precluded a serious discussion of how consumer


29

attitudes change over time. This perspective corresponds to the recent trend in decision

analysis and marketing. There, preferences (or goals) are treated as being constructed by

making choices rather than choices which are made on the basis of existing preferences

(e.g., March, 1978; Devetag, 1999; Payne, Bettman, and Johnson, 1992; Carpenter and

Nakamoto, 1989).

One venue that firms can take to actively change consumer preferences in their

favor is advertising. Galbraith (1958, 1988) argued that the role of advertising becomes

very important in the industrialized economy since the basic needs which inspired the

traditional economic thinking are already fulfilled. In fact, Schumpeter (1934) also noted

the constructive nature of preferences. In the discussion of the entrepreneur, he said:

“Yet innovations in the economic system do not as a rule take place in such a way that first new wants arise spontaneously in consumers and then the productive apparatus swings round through their pressure. We do not deny the presence of this nexus. It is, however, the producer who as a rule initiates economic change, and consumers are educated by him if necessary; they are taught, as it were, to want new things…” (p. 65)

This study shows that, in addition to good quality, producers also have to carefully

consider how to deliver their innovative products to consumers. Professional

endorsement is one way to significantly increase consumers’ confidence about the novel

products. Its effects cascades into high levels of replication of the design and exploitation

of the conceptual basis of the idea behind the innovation. Advertising constitutes another

promotion strategy concept for according consumers a greater role in the legitimization

of new racket designs.

VII. CONCLUSION

This paper suggests us to consider demand factors such as star endorsement, and

opinion- leader behavior as a key factor in accounting for the emergence of dominant

designs.


30

Compared to the existing literature on technological evolution, this study,

therefore, takes a more balanced view in that it brings unsuccessful innovations under

scrutiny. By doing so, the study not only presents technological evolution in the tennis

racket industry closer to the reality, but also provides a setting in which we can

illuminate some issues that improve our understanding on the process of technological

development. This study describes the cases where some racket designs became extinct

even though their quality was at least as good as successful ones. Empirical analyses

suggest that, in addition to innovation quality, such promotional strategies as professional

endorsement significantly improves the chance of an innovation’s success.

It is surprising to note that only one side of the market, the producer side, has

been extensively explored in previous studies. Figure 4 reiterates the need to jointly

consider both supply and demand conditions, and to view producers and consumers in

interaction with each other. That interaction conditions the success and failure of

innovations and the route that technological trajectories undertake.


While it is not explicitly stated, it is assumed in previous studies that the benefit

of an innovation is self-evident to consumers and they know what they want. So the

main target for the firm is to discover what they want and satisfy it with a good product.

However, as emphasized by Galbraith (1958), Schumpeter (1939), and March (1978),

innovators should exert a significant amount of effort to persuade consumers by

providing relevant information through various means, because the success of an

innovation emerges out of consensus among producers and consumers. The punch line of


31

this paper, therefore, is an invitation to adopt a more fully specified model that

incorporates also consumer considerations in the rise and fall of dominant designs.

It should be pointed out that the tennis racket industry and the sporting goods

industry, in general, have some peculiarities that are at variance with other industries.

The high visibility of professional players as a way to highlight consumer aspects and

technological innovation provides an ideal setting for this study. In addition, since the

conservative nature of the sport makes it more difficult for entrepreneurs to introduce

new ideas, the importance of entrepreneurial skills other than technological ones is well

highlighted. However, the industry seems very vulnerable to the ebb and flow of fads in

products rather than to substantive changes in technology. While recent studies suggest

that the endorsement by and the relationship with prominent players in the industry have

significant effects on the fate of patents and projects (e.g., Podolny and Stuart, 1995), we

also need to find out the limits under which endorsement effects effectively work.


32

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36

[ Table 1 ] Description of Variables

Variables

Description

Environment Characteristics

- Size of Tennis Playing Population - Number of Racket Manufacturers - Number of Rackets - Number of Rackets with Focal Design - Regulatory Change in 1981

: The number of people playing tennis regularly : The number of tennis racket manufacturers : The number of tennis rackets available in the market : The number of tennis rackets with focal design (i.e., oversize) : Dummy variable for change in rules on tennis rackets by the International Tennis Federation in 1981

Firm Characteristics

- New Entrant - Diversified - U.S. Ownership

: Whether a firm is a new entrant or an incumbent (1=Entrant; 0=Incumbent) : Whether a firm has related businesses (1=Diversified; 0=Single Business) : Whether a firm is an American or a foreign entity (1=American; 0=Foreign)

Design Characteristics

- Professional Endorsement - Design Quality (Playability) - Advertising

: The number of top professional players (top ten male and female players and semi-finalists in Grand Slam tournaments) who use rackets with focal design : Design quality measures (Overall racket performance measure by playtest panels) : The amount of advertising appearing in Tennis magazine

[ Table 2 ] Results of Experiment with Three Rackets

27 Inch Wood Racket 27 Inch Graphite-Composite Racket

29 ¼ Inch Graphite-Composite Racket

Average Speed of Serves 122 m.p.h. 124 m.p.h. 126 m.p.h.

Accuracy of Serves 60% 52% 80%

Source: Tennis, March 1997.


37

[ Table 3 ] Correlation among Different Measures of Racket Attributes

Variables Lab Test Male Testers Female Testers

Mean S.D. 1 2 3 4 5 6 7 8 9 10

Lab Test

1. Stiffness 5.31 1.57

2. Stability 6.88 1.82 0.2**

3. Power 7.30 1.87 0.2* 0.6**

Male Testers

4. Stiffness 6.75 1.05 0.4** 0.1 0.1*

5. Stability 6.99 1.04 0.3** 0.4** 0.3** 0.6**

6. Power 7.11 1.00 0.2** 0.5** 0.5** 0.3** 0.6**

7. Playability 6.81 1.05 0.1* 0.2** 0.2** 0.4** 0.6** 0.6**

Female Testers

8. Stiffness 6.45 1.28 0.3** -0.1 -0.2** 0.4** 0.3** 0.2** 0.2*

9. Stability 6.64 1.25 0.3** 0.3** 0.1 0.3** 0.4** 0.3** 0.3** 0.6**

10. Power 7.35 1.01 0.3** 0.1 0.1* 0.3** 0.3** 0.3** 0.2** 0.3** 0.5**

11. Playability 7.00 1.17 0.1** 0.1* 0.1* 0.3** 0.3** 0.2** 0.4** 0.2** 0.6** 0.6**

* p < 0.05, ** p < 0.01


38

[ Table 4 ] Poisson Regression of Racket Design Replication‡ ( from 1981 to 1992 )

Variable Model 1 Model 2 Model 3 Model 4

Intercept 29.714***

(6.081) 31.248***

(6.437) 24.501***

(8.596) 52.023***

(11.655) Environment Characteristics

Tennis Playing Population/1000 0.000

(0.000) 0.000

(0.000) 0.000**

(0.000) 0.000**

(0.000) Number of Racket Manufacturers -2.188***

(0.485) -2.323***

(0.537) -1.988***

(0.760) -3.770***

(0.992) Number of Racket Manufacturers 2 0.032***

(0.008) 0.034***

(0.008) 0.030**

(0.012) 0.063***

(0.017) Number of Rackets 0.032***

(0.008) 0.034***

(0.008) 0.036***

(0.013) 0.074***

(0.020) Number of Rackets 2 -0.000***

(0.000) -0.000***

(0.000) -0.000***

(0.000) -0.000***

(0.000) Regulatory Change in 1981 1.177***

(0.201) 1.151***

(0.204) 0.931***

(0.230) 1.163***

(0.225) Innovator Characteristics New Entrant (1=Yes; 0=No) − -1.251**

(0.500) -0.963*

(0.511) -1.966***

(0.440) Diversified (1=Yes; 0=No) − 0.668

(1.318) 0.408

(1.149) -0.176

(1.542) Domestic Firm (1=Yes; 0=No) − -0.884

(1.182) -0.794 (0.786)

-0.466 (1.181)

Design Characteristics

Professional Endorsement − − 0.169*** (0.027)

1.108*** (0.184)

Design Quality − − 0.494

(0.583) 1.970***

(0.633) Advertising − − 0.950

(1.315) 4.678**

(2.147) Professional Endorsement x Design Quality − − − -0.698***

(0.145) Design 1 (Oversize) 5.635***

(0.998) 7.776***

(1.459) 5.152*

(2.686) 2.717

(2.864) Design 2 (Longbody) 1.099

(1.247) 1.986

(1.427) 1.257

(1.751) -0.850 (1.878)

Design 3 (Ergonomic) 1.878* (1.008)

4.674* (2.514)

3.042 (3.349)

0.122 (3.995)

Design 4 (Three String) 1.135 (1.123)

3.903 (2.454)

2.803 (3.101)

1.268 (3.851)

Design 5 (Convex Throat) 2.998***

(1.109) 4.828***

(1.627) 3.442

(2.952) 0.481

(3.220) Design 6 (Fan String) 0.474

(1.534) 1.448

(1.692) 1.284

(1.719) -0.408 (1.846)

Design 7 (Widebody) 4.301***

(1.161) 5.173***

(1.240) 4.061*

(2.275) 0.563

(2.626) Design 8 (Tension Adjustable) 0.000

(0.000) 0.000

(0.000) 0.000

(0.000) 0.000

(0.000)

Log Likelihood 681.87 684.96 692.02 699.54

* p < 0.10; ** p < 0.05; *** p < 0.01 ‡ Playability is used for design quality. The numbers in parentheses are empirical standard errors.


39

[ Figure 1 ] Number of Racket-related Patents

[ Figure 2 ] Change in Dominant Designs

0

20

40

60

80

100

120

1954 1956 1958 1960 1962 1964 1966 1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998

Year

Num

ber o

f Pat

ents

Issu

ed

Keyword Search by "Tennis Racket" or"Tennis Racquet"Class 273/73+

100%

59%

47%34%

39%

36%

13%

17%

32%

12%

77%

37%

61%

94%

60%

38%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1956 - 1965 1966 - 1970 1971 - 1975 1976 - 1980 1981 - 1985 1986 - 1990 1991 - 1995 1996 - 1998

Period

New

Rac

ket I

ntro

duct

ion 6. comp - over - wide - LONG

5. comp - over - WIDE - regular4. comp - OVER - regular - regular3. COMP - small - regular - regular2. METAL - small - regular - regular1. WOOD - small - regular - regular Miscellaneous

1

2

3

4

5

6

material - head - width - length


40

[ Figure 3 ] A few examples of radical innovations


41

[ Figure 4 ] Product Innovations as a Function of Producer and Consumer Conduct

Advertising, Endorsements,

Sales Reviews, Star

Producers

Consumers


42

( Endnotes )


43

1 It should be noted that a new tennis racket with a focal racket design introduced by the firm who developed the design was excluded from the subset for the racket design since our main interest was the adoption of a racket design by competing firms. For example, an oversize racket introduced by Prince, the pioneer of this design, was eliminated from the oversize subset. 2 These designs were selected based on content analysis of racket reviews in popular magazines. We also conducted sensitivity analyses by including additional designs on the list. The results did not change the basic premise of our study. 3 The first dimension was ‘stiffness.’ It was the measure of the amount that racket frame bends during impact. While it was measured in pounds/inch in the lab, the numbers reported in the magazine was a relative scale, of which higher number means the racket was stiffer.

The second dimension was ‘stability,’ which measured the ability of a racket to resist the twisting motion with off-center hits. The unit of measurement was inch-pounds/degrees. As in the case of stiffness, the numbers reported in stability was also a relative scale. For example, one represented an absolute torsional stiffness of 10*(inch-pounds/degree) which was very flexible, while ten represented an absolute torsional stiffness of 100*(inch-pounds/degree) which was very stiff.

The last dimension was ‘power zone,’ which was the measure of the racket face area where the power exceeded a specified level of power. A racket with a higher number had a larger sweet spot. The total of 500 rackets were tested during the period from 1981 and 1995. While the test started in 1981, the sample included representative rackets introduced earlier than 1981. 4 We also tested the hypothesis with alternative measures of design quality: (1) an average of three attributes measured in the lab, (2) an average of three attributes measured on the court, (3) an index based on regression analysis of playability on three attributes measured in the lab, (4) an index based on regression analysis of playability on three attributes measured on the court, (5) an index based on factor analysis of three attributes measured in the lab, and (6) an index based on factor analysis of three attributes measured on the court. While the tables are not reported in the paper due to the limit on space, the main results are not qualitatively different from those in Table 4. 5 The results were not qualitatively different from those in the following even when we ran the same models based on one year comparison.

johannes ennings

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