the structure of adult friendship choices

The Structureof Adult Friendship Choices*

LOIS M. VERBRUGGE, University of Michigan

ABSTRACTThis paper examines bias toward status-similarity in adult friendships

in Detroit and a West German city. Principles of meeting and "mating," bywhich strangers are converted to acquaintances and acquaintances to friends,are stated. One of these, the proximity principle, claims that the more similarpeople are, the more likely they will meet and become friends. This principle istested in matrices of friendship choice for twelve social characteristics. Twostatistical measures of bias are used (odds ratio and marginal ratio) and theirproperties discussed. Compared to a random-choice model, adult friendshipsshow strong bias toward status similarity for all social characteristics. Bias isstrongest for "edge" categories of ranked statuses and for "best" friends. Theless similar two people are in social characteristics, the less likely they are to beclose friends. Demographic characteristics tend to show more bias towardhomogeneous choices than other characteristics. These findings are explainedand further analyses of adult friendship structure and dynamics are discussed.

Urban research has shown that friendship ties among adults are pervasiveand active, particularly when compared to neighbor and coworker ties(Axelrod; Bell and Boat; Bell and Force; Jitodai; Tomeh, a, b). These friend-ships are sources of social contact, intimacy, and assistance. They areconsidered primary ties, because of their emphasis on face-to-face contactand positive affect (Cooley; K. Davis; Parsons and Shils).

Despite friendship's prevalence and assumed importance, little isknown about the social structure of adult friendships. Who is chosen?What goods and services are exchanged? How large and heterogeneousare friendship networks? In this paper, one feature of these primary ties isexamined: the structure of friendship choice.

Most studies of friendship choice involve children or young adults,often college students (Lindzey and Byrne). There are relatively few re-ports of friendship choice by adults (Barnes; Berkun and Meeland; Curtis;Ellis; Gans, a, b; Greer; Kahl and Davis; Laumann, a, b; Lazarsfeld and

*I thank E. O. Laumann and F. U. Pappi for use of the Detroit and Altneustadt data sets.Laumann was principal investigator of the Detroit study; Laumann and Pappi, of the Alt-neustadt study.

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Merton; Lipset et al.; Loomis; Lundberg and Steele; Michelson; Richard-son; Riley and Foner; Rosow; Suttles; Williams; Zander and Havelin).Without exception, they find that adult friendships are highly homoge-neous in social and demographic statuses, attitudes, interests, intelligence,and personality traits, and that observed homogeneity is higher thanexpected, on the basis of a random-choice model. Most of these studiesexamine homogeneity for only one social characteristic. Exceptions areLaumann, Lazarsfeld and Merton, and Loomis.

These results are based on tables which cross-classify respondents(egos) by their friends (alters), for categories of a social characteristic. Thedata in the matrix are the outcome of processes of friendship formation,which have converted some strangers to acquaintances and some acquain-tances to friends. Many factors affect chances that strangers meet and thatacquaintances develop a friendship.

In this paper, we review factors involved in meeting and "mating,"state hypotheses about adult friendship choice based on them, construct amodel of expected choices to compare with observed ones, and test thehypotheses on two data sets.

Meeting and Mating

Social roles, life styles, attitudes, and personality traits channel individu-als' spatial movements and interpersonal preferences. Consequently, pairsof strangers have varying probabilities of ever meeting each other, andvarying probabilities of developing a close friendship if they do meet.I Thesociologist's task is to measure the real-world probabilities for meeting andfor mating (conditional upon meeting) and to identify the social principlesbehind them.

What plausible principles are involved in adult friendship forma-tion? We must rely on a speculative literature to identify them, since thereare no empirical studies on the meeting and mating processes themselves(i.e., how acquaintanceships formed in a population of adult strangers, orhow acquaintanceships were transformed into friendships).

Meeting. The most plausible principles for meeting are status-homo-geneity and spatial proximity. Strangers with similar social roles and beliefsare more likely to be in the same place at the same time, than those withdifferent roles and beliefs. Also, people whose daily rounds intersect aremore likely to become acquaintances than others.

Mating. While meeting depends on opportunities, mating dependson both attraction and opportunities. How readily an acquaintance is con-verted to close friendship depends on how attractive two people find eachother and how easily they can get together.

What factors influence attraction between two acquaintances? Ad-

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ams argues that people value consensus in their friendships above all else.Since consensus is more likely among status-similars than status-dissimi-lars, this principle should result in high status-homogeneity in friendshipdyads. Social psychologists have proposed other personality, cognitive,social learning, and social exchange factors to explain attraction (Marloweand Gergen). Among them are need-complementarity (Winch); balancetheory (Heider; Newcomb); congruence (Secord and Backman); feelings ofgain or loss in esteem (Aronson and Linder); valuation of rewards andcosts, or social exchange theory (Homans; Thibault and Kelly). The relativeimportance of these factors for adult friendships is not known, nor howthey are reflected in a dyad's social characteristics.

Opportunities for acquaintances to become friends are enhanced byspatial proximity. Close residence and daily rounds which intersect give ac-quaintances more chance to become intimate (Festinger et al.; Newcomb).

In summary, the literature repeatedly points to one sociologicalprinciple for meeting and mating: similarity in social status or spatial loca-tion. We call this the principle of proximity and state it as follows: the moresimilar in social positions two people are, the stronger their chances ofmeeting and becoming friends (cf. Brown). When referring to social sta-tuses, the notion of proximity is identical to that of social distance. Firstproposed by Simmel, the concept of social distance has been used often toexplain subjective choices (e.g., Bogardus, a, b; Laumann, a), but seldomfor objective (real) choices.

How important is the proximity principle in meeting, and in matingafter meeting? To answer these questions, we need three types of data:characteristics of a pool of strangers, of acquaintance dyads (both mem-bers), and of friendship dyads (both members). For large populations, theacquaintance data are necessarily unknown. Information about all acquain-tances is too vast to seek, even from a sample. Nevertheless, with the dataon strangers and friendship choices, we can answer a more general ques-tion: How strong (overall) is the principle of proximity in adult friendshipchoice? (We simply cannot measure the relatiave importance of proximityfor meeting and mating.)

This analysis focuses on the outcomes of opportunity and attractionfactors, not the processes themselves. We measure the importance ofproximity in friendship choice as reflected in social positions. We shallsuggest the opportunity and attraction factors underlying the results butdo not measure them directly.

Data Source

Two cross-sectional sample surveys of adult populations are used: the 1966Detroit Area Study and a 1971 survey in a West German city (population

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20,000), called Altneustadt (a pseudonym). The Detroit data contain 1,013cases of white males, aged 21-64. Details of sampling procedures used arein Schuman. The Altneustadt data contain 820 cases of males and females,ages 18 and above. The study used a single-stage, systematic probabilitysample of the municipality's eligible voters in 1971. Further details of thetwo cities and the samples appear in Verbrugge (53-56).

In both studies, the respondent was asked to name his or her threeclosest (dearest) friends outside the household. 2 In the all-male Detroitsample, only nominations of male friends were allowed. In Altneustadt,respondents could name male or female friends. (For males, the percent ofsame-sex nominations varies from 87 to 90% for the three friends. Forfemales, the percent of same-sex nominations is 62-68%.) Detroit respon-dents were more likely to name exactly three friends. Their average num-ber is 2.9, compared to 2.7 in Altneustadt.

In this analysis, Altneustadt men and women are pooled. Thisassumes that patterns of friendship choice are similar for the sexes (i.e.,there are no interaction effects by sex). All tabulations were done sepa-rately by sex, and the assumption was supported.

The two data sets are used for replication, not for cross-nationalcomparison. If our hypotheses are general, they should be supported in (atleast) two sites. This proves true in the analysis. Exceptions are notedwhen they occur.

Variables (or Social Positions)

Respondents were asked about several social positions of their friends. InDetroit, these are friend's occupation, employment status (self-employedor not), educational attainment, political preference, religious preference,nationality, and age. In Altneustadt, they are friend's occupation, employ-ment status, political preference, religious preference, age, marital status,sex, and length of residence in the city. The same items were obtained forrespondents.

All variables are coded in categorical form for this analysis. Choosingcategories is a serious task (cf. Blau and Duncan, 24). Categories shouldrepresent real social groupings, people who share a distinctive attribute.Category members are assumed or known to behave more like each otherthan like other categories' members. Here, we gave careful thought tofinding categories that are more than simply conventional in social re-search, but whose members have differential social behavior.

Social statuses were divided into categories as follows: Current ormost recent occupation is coded according to the International StandardClassification of Occupations (International Labor Office). The five-digitcodes were collapsed to the six major groups of the classification. Cate-

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gories for housewife (Altneustadt) and student (both sites) were added tothe six groups. The detailed occupation titles are also assigned interna-tional prestige scores according to Treiman's scheme. Prestige scores areviewed here as attributes of individuals, rather than of the jobs they hold.The continuum is split into six categories.

Education is coded as years of completed schooling. The categorieschosen reflect important boundaries in educational attainment, whethera diploma or degree is achieved or not. Nationality for Detroit is codedfrom questions on origin country and origin language. The categories areregions which have well-documented cultural differences and differentperiods of immigration into the United States. Residence length for Alt-neustadt is based on two features: migrant status (a dichotomy) and yearsof residence in the city. The latter is split into two categories to provide areasonable boundary between recent and long-term residents. Residencelength is asked only if ego's friend lives in the municipality.

Age is split into ten-year groups, assuming they roughly differen-tiate stages of life cycle and associated activities. One exception occurs:ages 20-29 are split into two five-year categories. The early twentiesusually entail fewer job and family responsibilities than the late twenties,and these differences may be reflected in friendship choices.

Political preference, religious preference, sex, and marital statushave standard categories in the two sites. A variable combining sex andmarital status is also used, to determine if friendship choice is even morediscriminating for sex—marital status than for either variable alone.

Most of these categories are real social divisions with documentedbehavioral consequences. People perceive the categories named and, weassume, respond to them in choosing friends. Caution must be exercisedfor three variables in which categories have been imposed on continuousvariables: occupational prestige, age, and residence length. Although webelieve that behavior within these categories is more homogeneous thanbetween categories, the boundaries named are not necessarily sociallyrecognized ones.

The survey questions and further coding details are in Verbrugge(62-78, Appendix II).

Methodology: Choosing a Model and Measuring Bias

For each social position, a cross-tabulation of ego categories versus altercategories is prepared. A separate matrix is made for each Friend (1,2,3).Altogether, 54 matrices are used in this analysis.

To measure how strong the proximity principle is, we need to con-struct a model matrix for comparison with the actual one. The modelmatrix shows an expected distribution of friendship choices, which emerge

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from the initial pool of strangers. The difference of observed choices fromexpected ones is called "bias."

There are two ways to build the expectations matrix. First, if atheory or prior empirical data provide numerical probabilities of choice (offriends from strangers), these can be used to construct a set of expecta-tions. The closer the observed matrix fits the model one, the more valid thetheoretical model which provides the probabilities. Second, if strong the-ory or prior data are lacking, a conservative approach is recommended.One assumes that friendships are formed by random pairings of strangersand constructs a matrix to reflect that. Then, one determines whetherobserved choices deviate significantly from it and whether the pattern ofdeviations fits hypotheses.

There is no prior research or theory which justifies a set of numericalprobabilities for adult friendship choice. This analysis is exploratory anduses a simple random-choice model. It is an exceedingly naive model ofsocial choice. Few social behaviors fit such a model, or should be expectedto fit one! Nevertheless, it is often a first step in finding patterns in data,from which nonrandom models are built. 3

The measure of bias one chooses determines how the random choicemodel is constructed. Here, we use two measures of bias: an odds ratioand a marginal ratio.

The odds ratio compares the odds that egos in category i choosesame-status friends to the odds that other egos (not i) choose friends incategory i. For a 2 < 2 table, the odds ratio is (FiiF22 / F12 F21 ) (Mosteller).An n x n table can be collapsed to 2 x 2 tables in numerous ways to testdifferent hypotheses. For example, to examine the tendency to choosesame-status friends, this odds ratio is computed: [F21 (F.. — F,. — F. i + FL1 )/

(F,. — F11 ) (F, — F12 )]. For each matrix, a total of I such odds ratios arecomputed. The odds ratio has a desirable feature: it is invariant with rowor column multiplications (i.e., not sensitive to its margins).

Observed odds ratios can be compared with expected ones to mea-sure bias. Constructing a random-choice model is straightforward. For thatmodel, the expected value for the odds ratio is 1.00 in all cases. This meansindependence of the two stubs. Observed odds ratios are tested for statis-tical significance (difference from 1.00) by the procedure outlined in Good-man (4-13).

The marginal ratio states how much more egos in category i choosesame-status friends than category i friends appear in the population ofeligibles (strangers). For the marginal ratio, we first compute the percent-age distribution of choices within rows. The ratio of observed percent to anexpected percent measures bias. 4 The marginal ratio is identical to thesocial distance mobility ratio found in analyses of occupational mobility. Itis affected by row and column marginal distributions (Blau and Duncan;Tyree). This feature hinders comparison of matrices with different marginal

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frequencies and even comparison of cells within a matrix.sFor the marginal ratio, we use the bottom marginal of the matrix for

the random-choice expectations. This is the distribution of friends for asocial position. The model therefore claims that egos of each categorychoose their friends from the friend population at random, i.e., that thepercentage distribution in each row is identical to the bottom marginal. Notest of statistical significance for the ratio is available.

Both the odds ratio and the marginal ratio are acceptable measuresof bias, compared to a random-choice model. As conceived here, they bothuse the friendship matrix itself to identify the population of strangerseligible for friendship. 6 We prefer the odds ratio because of its desirablestatistical properties. In this analysis, when both the odds ratio and mar-ginal ratio were computed, we report only the former.

Hypotheses

The Detroit and Altneustadt data permit examination of friendship choicein three dimensions: (a) for different social positions, (b) for categories ofsocial positions, and (c) across friends by their nomination order.

HOMOGENEITY BIAS

Same-status people are very likely to choose each other as friends, more sothan if friendship choice were random (Hypothesis 1). This is the onlyhypothesis to be stated which has prior theoretical and empirical atten-tion. 7 Similarity in social positions is probably valued because viewpointsand experiences associated with them are similar. The more uniformly andcomprehensively a position reflects such features, and the more salientthey are, the more likely it is a strong basis for friendship choice (cf. Byrne;Newcomb).

HOMOGENEITY BIAS WITHIN SOCIAL POSITIONS

If homogeneity bias is truly pervasive as a principle of friendship choice, itshould appear for every category of social positions (Hypothesis 2a).

It is likely that some social groupings have greater bias toward same-status friends than others. We hypothesize that, when categories can beranked (e.g., age), homogeneity bias is greatest for "edge" categories(Hypothesis 2b). Edges are the highest and lowest categories. This has beenfound true in research on occupational mobility (Blau and Duncan), friend-ship choice (Laumann, a, b), and age homogamy of brides and grooms(McFarland).

The edge effect may be substantive (i.e., sociologically interesting)

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Adult Friendships 1 583

or artifactual. There are two substantive reasons for it: first, edge categoriesare often small and edge members uncommon. As rare people, they maybe particularly envied, disdained, or respected in society. This recognizedspecialness may encourage self-consciousness and solidarity among edgemembers, and it may enhance preference for each other as intimates.Chances of meeting each other may also be increased if they have moresimilar roles and leisure activities—due to discrimination or choice—thanother categories. Second, edge people can choose same-status friends ordifferent-status friends, but the latter exist in only one direction. If theproximity principle is a strong one, edge people have limited options forfriendship choice. They bump against constraints in one direction. Theymay compensate by choosing more same-status friends, which inflatestheir homogeneity bias.

But the edge effect can be artifactual when simple ratios of twonumbers are used to measure bias (e.g., the marginal ratio). Small numera-tors and denominators easily produce very large, or very small, ratios.Edge categories are often small, and high bias may simply reflect thatfeature. A second artifact can actually deflate bias for the edges. When edgecategories are open-ended, they often contain a greater span of codes thanmiddle categories. In our data, this is true for age (the upper edge for bothegos and alters, the lower edge for alters only), education (17+ years),length of residence (10+ years), and occupational prestige (70+). Thewider a category's span, the less biased toward homogeneity its choiceswill appear. There is no obvious way to correct for these artifacts: if weassign every category the same width, the cell sizes for edges become verysmall and incur the size artifact.

If Hypothesis 2b is supported, we must determine which of theabove reasons accounts for it.

Hypothesis 2b refers to ranked statuses. But the rareness conceptcan be generalized to accommodate non-ranked statuses as well: small, self-conscious groupings will show greater bias toward homogeneous friend-ships than other groupings (Hypothesis 2c). Minorities may develop a senseof collective solidarity due to discrimination, rare skills, or distinct culturaltraditions. This will encourage greater homogeneity bias in their friend-ships than we find in other categories. Despite the simplicity of thishypothesis, there is no prior example of it in literature on friendshipchoice. Clearly, a simple ratio measure is likely to produce artifactualresults for this hypothesis (due to the category size problem).

HOMOGENEITY BIAS ACROSS FRIENDS

In Detroit and Altneustadt, first-named friends tend to be best friends. Theaverage degree of affect felt by ego toward a nominated friend decreasessharply from Friend 1 to Friend 3 (Verbrugge). If having similar attitudes

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and concerns is highly valued in friendship, then people will strive to findstatus-similars for their very best friends. For weaker friendships, they willbe less concerned about a close match (cf. Levinger and Snoek). Homo-geneity bias should decrease across friends by nomination order (Hypothe-sis 3), or any other indicator of primariness. If the principle is very strong,this differential bias should appear even in data on one's three closestfriends.

PROXIMITY BIAS WITHIN SOCIAL POSITIONS

Hypotheses 1 and 2a-2c focus solely on the diagonal cells of a friendshipmatrix. The proximity principle also allows deductions about off-diagonalcells. Hypothesis 4 refers to ranked social positions: the less similar twopeople are in their daily rounds, skills, attitudes, domestic commitments,and social esteem, the less likely they will meet or form a close friendship.Bias should be greatest in the diagonal cell and diminish as one movesfarther from it (i.e. as the friend's status is less similar to ego's).

Results

HOMOGENEITY BIAS

Table 1 shows the overall percent of same-status choices and degree of biasfor each social position. From a descriptive viewpoint, homogeneity inadult friendship is common. In Altneustadt, about 75 percent of adultschoose friends whose sex or marital status is the same as their own. InDetroit, about half of all friendships are age-homogeneous. For all social

Table 1. HOMOGENEITY AND HOMOGENEITY BIAS (COMPARED TO A RANDOM-CHOICE MODEL)IN FRIENDSHIPS, FOR ALL SOCIAL POSITIONS, DETROIT 1966 AND ALTNEUSTADT 1971

Social Positionand Site

Percent of Friends in SameCategory as Ego's

^FI,/F.. x 100

Friend 1 Friend 2 Friend 3

Degree of Bias (Marginal Ratio)

Observed CasesExpected Cases


OccupationDetroit 48.4 50.5 50.1 1.72 1.85 1.78N (1005) (997) (954)Altneustadt 48.3 45.9 42.4 2.43 2.25 2.14N (760) (737) (691)

Employment statusDetroit 85.4 84.9 82.2 1.09 1.09 1.05N (996) (989) (946)Altneustadt 86.0 83.3 83.1 1.07 1.04 1.03N (401) (377) (356)

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Table 1, continued


Percent of Friends in SameCategory as Ego's

EF;,IF,. x 100


Degree of Bias (Marginal Ratio)

Observed CasesExpected Cases


EducationDetroit 39.0 38.5 36.7 1.87 1.77 1.67N (1005) (997) (954)

AgeDetroit 51.4 49.4 45.8 2.45 2.36 2.20N (1003) (995) (951)Altneustadt 45.3 41.0 44.1 2.71 2.37 2.52N (755) (743) (689)

Marital statusAltneustadt 77.2 75.6 74.7 1.24 1.15 1.17N (760) (737) (691)

SexAltneustadt 78.2 74.1 75.1 1.58 1.50 1.52N (760) (737) (691)

Sex-Marital statusAltneustadt 61.1 56.9 57.5 1.98 1.75 1.81N (760) (737) (691)

NationalityDetroit 42.4 43.4 40.2 1.58 1.67 1.53N (889) (865) (810)

Political preferenceDetroit 60.6 62.1 56.0 1.53 1.54 1.39N (891) (870) (837)Altneustadt 45.9 42.1 39.4 1.68 1.56 1.55N (760) (737) (691)

Religious preferenceDetroit 69.4 64.6 63.9 1.56 1.47 1.45N (975) (966) (920)Altneustadt 74.4 70.8 72.1 1.28 1.23 1.25N (739) (723) (666)

Residential mobilityAltneustadt 54.0 51.7 49.9 1.59 1.49 1.46N (498) (439) (379)

Occupational prestigeDetroit 39.4 42.9 41.1 1.55 1.60 1.54N (995) (987) (936)Altneustadt 41.9 44.1 41.1 1.74 1.77 1.72N (413) (388) (370)

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positions in the two sites, at least 35 percent of all friendships are homo-geneous.

No odds ratio is appropriate for Hypothesis 1, so we must rely onthe marginal ratio. Hypothesis 1 is strongly supported. The observednumber of pairs in diagonal cells is compared to the expected numbercomputed from the alter marginal. In all 54 matrices, the marginal ratioexceeds 1.00. Apparently, all of the social positions are salient for friend-ship choice. Whether because of high chances of meeting people with thesame social or demographic characteristics, or strong attraction to similaracquaintances, adults are much more likely to have same-status friendsthan if they were to choose friends at random.

HOMOGENEITY BIAS WITHIN SOCIAL POSITIONS

Table 2 shows the percent of same-status choices and degree of bias foreach category of the social positions. The degree of homogeneity is re-markable for several categories. Over 60 percent of friendships are status-homogeneous among production workers (Detroit), students, workerswho are not self-employed, young adults, single and married people,males and females, married males, Republicans and Democrats, peoplewith no political preference (Altneustadt), Catholics, Jews, and Protestants(Detroit).

Table 2. HOMOGENEITY AND HOMOGENEITY BIAS IN FRIENDSHIPS, BY CATEGORIES OF SOCIALPOSITIONS, DETROIT 1966 AND ALTNEUSTADT 1971.


Friend 1*

PercentHomogeneous Odds

Choices RatioSocial Positionand Site

Friend 1'


Choices Ratio

Occupation Sex—Marital status

Detroit AltneustadtProfessional 48 5.87 Single male 57 20.53

Administrator 33 3.00 Married male 85 15.55

Clerical (9)t [1.67]t Prev. married male (5) [5.82]

Sales 28 5.23 Single female (24) 5.02

Service 31 16.73 Married female 53 12.49

Production 63 4.83 Prev. married female 33 8.15

Student (100) § NationalityAltneustadt Detroit

Professional 63 12.26 North American (18) 5.11

Administrator (28) 11.22 British 47 2.25

Clerical 35 3.64 West/North 42 2.19

Sales (9) [2.28] East European 46 5.26

Service (11) [6.50] South European 29 7.00

Production 50 6.49 Other (41) 27.04

Housewife 52 7.81 Political preferenceStudent 70 74.29 Detroit

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Table 2, continued


Friend 1*


Choices RatioSocial Positionand Site

Friend 1


Choices Ratio

Employment statusDetroit Republican 56 5.48

Self-employed 44 7.64 Independent 35 5.68

Not self-employed 90 7.64 Democrat 75 4.75

Altneustadt Altneustadt

Self-employed 44 7.31 Christian Democrat 45 5.88

Not self-employed 91 7.31 Liberal (Free Democrat) (17) 72.20

EducationSocial Democrat 43 4.59

DetroitNo pref./Don't know 72 3.40

0-8 years 27 5.02 Religious preference

9-11 29 3.47 Detroit

12 54 2.23 Catholic 68 6.28

13-15 31 4.03 Protestant 74 7.57

16 39 5.98 Jewish 83 643.9

17 or more 49 14.22 None/Other (12) 6.36

Age Altneustadt

Detroit Catholic 86 6.83

Under 25 72 81.81 Protestant 52 6.79

25-29 46 18.32 None/Other (17) 14.10

30-39 51 6.44 Residential mobility40-49 58 4.98 Altneustadt50-59 45 6.82 In Alt. since birth 54 2.8760 or above 21 4.58 10+ years in Alt, 53 2.51

Altneustadt Less than 10 years 55 12.56Under 25 71 53.22 Occupational prestige25-29 36 6.79 Detroit30-39 56 7.28 1-29 19 2.7840-49 38 3.18 30-39 48 2.2650-59 34 4.21 40-49 33 2.5560-69 35 6.25 50-59 40 2.5170 or above 38 15.15 60-69 30 8.01

Marital status 70+ 43 26.94Altneustadt AltneustadtSingle 72 25.58 1-29 34 7.20Married 84 6.89 30-39 (15) [2.65]Previously married 29 5.60 40-49 57 3.11

Sex 50-59 37 2.55

Altneustadt 60-69 36 4.55

Male 90 19.18 70+ 38 16.55

Female 68 19.181

*Detailed data are shown for Friend 1. Data for Friends 2 and 3 are available on request.

t( ) means n < 10.

$[ ] means the odds ratio is not significantly different from 1.00 at p w .05. The criterion values forsignificance are in Goodman (Table 3).

§Cannot be computed because of a zero cell in the 2 x 2 table.

IA table which is originally 2 x 2 produces only one odds ratio.

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588 I Social Forces / vol. 56:2, december 1977

Hypothesis 2a is strongly supported. Bias toward homogeneity ispervasive, appearing in virtually all social categories. All 240 odds ratiosexamined exceed 1.00, and all but 15 of them are significantly differentfrom 1.00. 8 We infer that virtually all the categories are good cues ofpeople's daily rounds (which affect chances of meeting) and of concernsand attitudes which people want to have in common with friends.

Where is this bias strongest? Odds ratios are routinely above 10.0 forstudents and professionals; highly educated people (17+ years); youngadults (under 25 and 25-29) and adults 50-59 (Detroit); males and females;married men and married women; Catholics, Jews, and Protestants (De-troit). This means that the chances a respondent in category i chooses asame-status friend are over ten times the chances that other respondentschoose friends in category i.

The excess choices occur because of unusually high opportunitiesfor these categories to meet status-similars and/or very strong preferencesto have friends of the same status. For example, students often live indormitories or in common residential areas, and they have common con-cerns and leisure interests. These enhance chances that students will meetother students and want them for friends. Reasonable explanations can beadvanced for most of the other categories with high homogeneity bias.

But the data require more systematic attention. Do edge categoriesshow stronger bias than middle ones? Do small categories show strongerbias than large ones? If Hypotheses 2b and 2c are confirmed, can webelieve these are sociologically interesting results?

The edge hypothesis (2b) is tested for education, age, and occupa-tional prestige by asking if the two edge categories have the highest biasmeasures in a table. Of 15 tests for the odds ratio, the hypothesis isconfirmed 7 times. But the failures show an interesting uniformity: thecategory adjacent to the highest-bias edge ranks second; the opposite edgeranks third.

In summary, the highest bias for same-status friends appears forpeople of highest education, youngest age, and highest prestige. Some-times, the people with almost-highest education (16 years), almost-young-est age (25-29), and almost-highest prestige (60-69) rank next to bias forsame-status friends; the opposite edge ranks third. 9 Otherwise, the oppo-site edge ranks second.

Why do these particular categories have highest bias? If we canshow generally that when people choose a friend different in education orprestige, they bias choices toward better-educated and higher-prestigepeople than themselves, the answer is clear. The highest-status peoplebump against constraints (there are few people higher than themselves)and they compensate by additional choices of same-status friends. Simi-larly, if people prefer younger friends (when they choose an age-dissimilarone), the fact that bias is greatest for the age group under 25 is explained.

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To test this, we use all middle categories, since they provide cells toboth left and right. For each category, above-diagonal and below-diagonalcells are pooled. This odds ratio is computed: the numerator is the oddsthat egos in category i choose a higher-status (including older) friendinstead of a lower-status (including younger) one. The denominator is thecomparable odds from the marginal, reflecting the relative eligibility ofupper- (> i) and lower- (< i) status friends. Odds ratios above 1.00 meanthat egos of category i are biased toward choosing upper-status friends.Altogether, there are 63 tests. Bias for more-educated, higher-prestige, andolder friends appears in 64 percent of the tests. But the results are complex:The odds ratios tend to be below 1.00 for low-status egos (i.e., a bias towardlower-status friends) but increase monotonically and exceed 1.00 above athreshold category. Egos with education 11+ years, with occupationalprestige scores 50+, and aged 40+ all show preference for higher-statusfriends. Thus, bias for upper-status friends is not pervasive. It appearsamong middle-status egos and becomes stronger as ego's status increases.In fact, low-status egos who have a dissimilar friend tend to choose a lower-status person than themselves. This is especially true for age.

The number of choices made to right and left of the diagonal de-pends partly on the span of codes available, i.e., on the social distance ofeligible friends. A fairer test of upward versus downward bias is to com-pare choices in the cells adjacent to the diagonal. This controls for socialdistance if we assume the adjacent categories have equal social distancefrom category i. When the test is performed for adjacent cells, results aresimilar to those above. Fifty-six percent of the tests show the expected bias,and the pattern is the same.

Thus, bias for dissimilar friends tends to be upward (toward older,more educated, more esteemed people) when ego's own status is middleor high. Bias for dissimilar friends tends to be downward for low-statusegos. These results are true even for adjacent cells (the two closest socialgroupings to ego's own). The strong patterns of social choice are intrigu-ing, especially for education and prestige: Do low-status people feel morecomfortable with their education (or prestige) inferiors? Are the motiva-tions of high-status people different, so they hope to enhance their ownstatus by associating with higher-status friends? Although interesting intheir own right, these patterns do not explain the initial question (whichedge category shows strongest homogeneity bias). Either edge can havehighest bias and be consistent with the patterns of choice just found fordissimilar friends.

In summary, the edge effects seem to have a sociological basis (edgepeople experience constraints in friendship choice). The results are notsimple, but they are so consistent in both sites that one must count them asreal and seek further explanations. There is no way to test the secondsociological explanation, that edge members have stronger preference for

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590 / Social Forces / vol. 56:2, december 1977

status-similar friends than middle-category members do.Could the results be artifactual? Probably not. Odds ratios are based

on four numbers and are less sensitive to small category sizes than themarginal ratio. Second, the category-width artifact tends to deflate oddsratios. Assuming it is present, the homogeneity bias of edge categories isactually less than if the artifact were removed.

To test the small-category Hypothesis (2c), we posit a negative associ-ation between category size and homogeneity bias. Kendall's tau-a (-r a) isthe test statistic. When T,, is computed for the ranks of odds ratios, withcategory size, the hypothesis is not supported. Of 45 tests, 47 percentproduce negative TQ , 7 percent a Ta = . 00 (no relationship), and 46 percenta positive T,,. We conclude that small social groupings are not more likely tohave high homogeneity bias.

The tau is a very demanding test for Hypothesis 2c. A more lenienttest involves just the polar categories: Do the smallest categories havehighest bias, and the largest categories, lowest bias? Of 45 tests for theodds ratio, only 40 percent support the first statement, and 27 percent thesecond.

In summary, there is little evidence that category size and homo-geneity bias are associated. (Even if an association were found, we wouldhave to demonstrate further that small groupings are more segregated orsolidary, which would enhance their chances of meeting and mating witheach other.)

HOMOGENEITY BIAS ACROSS FRIENDS

The hypothesis that homogeneity bias decreases as friendships becomeless close is tested for each social position and for their categories.

Using Table 1, consider the marginal ratio for the three friends. Biasdecreases across them for only 8 of 18 tests. (In addition, four tests almostmatch the hypothesis.) But for 12 tests, bias is greatest for Friend 1. Andfor no social position is bias greatest for Friend 3.

Applying the hypothesis to categories, there are 76 tests for theodds ratio. 10 Only 17 percent of the tests show the hypothesized decrease.But 57 percent of tests do show that Friend 1 has highest bias. (Friend 2 hashighest bias in 36% of the tests.) The results imply that status-similaracquaintances are more likely to be elevated to the ranks of best friendsthan dissimilar acquaintances.

Thus, Hypothesis 3 is not confirmed, but the results do show thatstronger efforts are made to find a similar person for one's very best friend(here, Friend 1) than for other close friends.

The social positions which show best friend bias most persistentlyare age, sex, marital status, political preference (Altneustadt), religiouspreference, and residence length. Apparently, it is more important to find

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a best friend whose life cycle status and political/religious commitmentsare similar, than one whose social status and ethnic background are similar.Differential opportunities to meet may also account for these differences.This is a very intriguing result; the relative importance of these socialpositions in adult friendship choice merits more research.

PROXIMITY BIAS WITHIN SOCIAL POSITIONS

To test Hypothesis 4, we scan odds ratios for each category of rankedpositions. (These are education, age, and occupational prestige.) Takingeach row, do the ratios decrease to the left and right of the diagonal cell?The hypothesis is considered supported only if the ratios monotonicallydecrease as we move from the marginal. Of 52 tests, 43 (83%) fit thehypothesis (data not shown). For each social position, the percent support-ing it are: 91 percent for education, 75 percent and 77 percent for age,100 percent and 83 percent for occupational prestige.'' (Detroit is reportedfirst, Altneustadt second.)

In summary, Hypothesis 4 receives ample support. The less similara pair of adults are, the less likely they are to become close friends. Inaddition, the pairs with very low bias indicate the relatively low chances ofmeeting and/or attraction for each other that people of very different socialroles, attitudes, and demographic status experience.

Discussion

Let us summarize the principal results. Adults choose friends of similarsocial status much more than a random-choice model predicts. This homo-geneity bias appears for socioeconomic and demographic characteristics,ethnic background, and political/religious preferences (Hypothesis 1). Itappears for virtually all social groupings, especially for edge categories(or next-to-edge categories) (Hypotheses 2a and 2b). Examination of off-diagonal choices suggests that edge-category egos experience constraintswhen choosing dissimilar friends: high-status egos would like higher-statusfriends, but the diminishing number of eligibles forces more same-statuschoices. Similarly, low-status egos seem to prefer lower-status friends, butthey end up choosing more same-status friends because of size constraints.Besides such constraints on choice, edge members may be very stronglyattracted to each other or have high chances of meeting. There is no way totest this second effect in the data sets. We have demonstrated that at leastone of the two hypothesized social effects occurs. And there is no evidencethe result is artifactual.

Hypothesis 2c is not supported: there is no convincing evidence thatsmall social groupings strongly prefer same-status friends. For the social

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statuses in the Detroit and Altneustadt data, minorities do not have greaterhomogeneity bias than other groups.

Homogeneity bias is strongest for first-named (usually "best")friends, compared to other close friends. This strengthens the evidencethat similar status is highly valued in friendships. The result differsslightly from Hypothesis 3.

Finally, the principle of proximity is strongly supported (Hypothe-sis 4). The more similar two adults are in social status, the more likelythey will be close friends, compared to a random model. As socialdistance increases, bias measures drop under 1.00 and tend to decreasemonotonically.

The main contribution of this analysis is evidence that social andspatial proximity are strong and pervasive factors in adult friendshipchoice. The choices are nonrandom and are patterned to fit the prox-imity principle. The social roles and preferences measured are crudeindicators of concerns, attitudes, pleasures, and dreams. Consensus onthese matters is probably the valued aspect of friendship, not the simi-larity in social positions themselves. The positions are also crude indi-cators of daily rounds and thus of chances of meeting. Despite theirindirectness, social positions manage to confirm the proximity principle.More direct measures of spatial location, daily movements, and lifeconcerns for egos and their friends would probably demonstrate it morestrongly.

The data leave no doubt that adult friendships are strongly strati-fied with respect to social statuses, attitudes, and demographic charac-teristics. Particularly striking is the strong bias for age, sex, and maritalstatus (see results for Hypotheses 2a, 3, 4). As expected, sex—maritalstatus tends to show higher homogeneity bias than either of its com-ponents, indicating that adults take the combination explicitly into ac-count when choosing friends. Apparently, demographic characteristicsare good indicators of important past experiences, perspectives, andinterests (Booth), and personal concerns. More formally: the experiencesencoded by age, sex, and marital status are salient and clearly reflectedthere, relative to other social positions. This accounts for high attractiontoward demographically similar friends (a mating effect). What aboutmeeting? Do daily rounds of people similar in age, sex, and maritalstatus intersect more than people of similar SES? We simply do notknow. Whatever the specific reasons for high bias toward demographi-cally similar friends, the data for age and sex confirm Mayhew's claimthat ascriptive characteristics remain important in modern societies.

This analysis complements Laumanri s (a, b) work on adult friend-ships. 12 In Cambridge—Belmont and Detroit, Laumann finds substantialdifferences among occupational and ethnoreligious groups in how theychoose friends. Here, we examine the chances that people become friends,

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for various social positions, and test one principle which accounts fordifferential chances. The analyses are distinctly different: Laumann studieshow similarly two categories spread their friendship choices among eligi-bles; we study how often people of two categories become friends, com-pared to a model of social choice. We demonstrate persistently that theproximity principle accounts for frequencies of pairs. The social structureof the data emerges clearly with a simple methodology.

Second, Laumann (a) finds the edge effect for occupation data inCambridge—Belmont. The Detroit data produce a similar result (Laumann,b). In this analysis, the edge effect is found for occupational prestige scores(a clearly ranked position) and all other ranked statuses available. Mostimportant, its interpretation as a social effect, rather than an artifact, isbuttressed.

Conclusions

Finding structure in empirical data is a prior step to constructing models ofsocial choice. In this first analysis, we have looked for structure with sev-eral modest hypotheses to guide the examination. Overall, the proximityprinciple is strongly confirmed. An appropriate next step is to use the em-pirical and theoretical results to make a nonrandom model. For example,using Table 2, we might state that same-category pairs will be twice asfrequent as a random model predicts (i.e., the expected marginal ratio is2.00) or has twice the odds of a dissimilar pair. A pattern of choice for off-diagonal cells can also be incorporated. 13 The model of expectations isthen compared to observed data and goodness-of-fit computed. Alterna-tively, real friendship dynamics can be observed and a pattern of probabili-ties derived from them can be tested on these matrices.

In addition to such analysis of friendship structure, important ques-tions about processes and consequences of adult friendships remain: first,is their structure principally the outcome of restricted opportunities formeeting, or of preferences and contact opportunities with acquaintances?In other words, what is the relative importance of meeting versus mating?To answer this, a matrix of acquaintanceships is required from cross-sec-tional or longitudinal data. Second, a mating model claims that peoplefilter acquaintances, preferring some for close friendship. Little is knownabout those preferences among adults. Specifically, what do adults valueand seek in their friendships? How good are social positions as cues ofthose desired features? Third, what are the expressive and instrumentalconsequences of homogeneous friendships? Speculation about expressivebenefits abounds (Adams; Brown), but evidence of any consequences isscant. The notion that homogeneous ties have instrumental disadvantages(Verbrugge) remains to be tested.

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Research on these topics will add to child and young adult studies,making possible a life cycle approach to friendship formation. Moreover, itwill demonstrate that adult friendships are not sociologically mundane, buthave detailed structure, complex dynamics, and numerous consequences.

Notes

1. Sociologists have rarely recognized that two conceptually distinct processes (meeting andmating) underlie friendship choices. An exception is Lazarsfeld and Merton. In their studiesof marital-mate selection, Romney discusses the need for two models and Eckland hints at it.A fine conceptual treatment of friendship dynamics, which includes meeting and matingprocesses, is provided by social psychologists Levinger and Snoek.2. Respondents were actually asked to name three people "who are your closest friends andwhom you see most often." This taps two dimensions (degree of affect and contact fre-quency). For this analysis, we would like the friends to be ordered by degree of affect.Examining the data, we find that most respondents do name friends in order from most toleast affect, and it is a more uniform criterion underlying nomination order than contactfrequency is (Verbrugge).3. Nonrandom models can be constructed in three ways. First, one can build a hypotheticalmatrix of choices, based on a theory about social choice. Romney's marriage analysis is of thistype. Second, one can choose a normative matrix of choices, a set of observed choices fromsome other time or place. After standardization of marginals, the researcher's data arecompared to this normative matrix. McFarland's marriage analysis is of this type. Third, log-linear models for contingency tables allow the researcher to specify effects for marginals andcombinations of them in a model (J. Davis). Complex models involving main effects, correla-tions, and interactions can be tested.4. To avoid rounding errors, it is best to compute the ratio of observed frequencies (F^) toexpected ones (ti). Computations were performed both ways for this analysis.5. The marginals problem is called a "group size problem" in the social networks literature(Bonacich; McFarland and Brown). Tyree proposes another measure of bias: Yule's Q. Q is aconsiderable improvement over the marginal ratio. But it is not totally free of marginal effectsand it has a clumsy interpretation.6. The expected distribution should refer to the population of strangers who are eligible forfriendship. The stranger population is impossible to define precisely, since friendship choicesare not restricted to those within the same population egos come from. (In fact, 12-19% of thenominated friends live outside the urban areas of Detroit and Altneustadt.) In addition, somestrangers are very active socially and very attractive, and they have higher chances of beingmet and liked by all types of egos than other strangers do. In other words, some strangers aretruly more eligible than others to become friends of any ego.

Lacking independent data on the strangers who are eligible for ego's friendship, weaccept the friend marginal distribution as a good guess. The friend marginal is assumed toreflect the structure of opportunities for friendship, taking into account the unequal chancesstrangers have of being met and liked by others and their wider boundaries than the egopopulation itself. We take the friend marginal as given. Bias in friendship choice is thenassessed. We do not intend to explain the differences between the ego and alter marginals,only the patterns within the table.

(Differences between the ego and friend marginals are discussed in Verbrugge, 64-66.Besides the two factors named above, response error may cause the two marginals to differ.Egos may systematically inflate their friends' social status when describing them in theinterview.)7. Hypotheses were also formed to compare the strength of homogeneity bias for differentsocial positions (age, occupation, etc.). However, the hypotheses are untestable due to afeature of the matrices: a matrix's order influences measures of choice and bias. The fewercategories, the more homogeneous choices appear to be and the less biased when comparedto any model. The remedy is to force all matrices to be the same order. (In our case, this wouldbe 2 x 2, the smallest matrix order.) The cost of condensing tables is great, since much

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information in the original table is thereby lost.8. There are 84 categories to consider, i.e., 252 odds ratios for the three friends. Notes (d) and(e) of Table 2 explain why only 240 are examined.9. One exception: in Detroit, the odds ratio shows this ranking for Friend 1's age: 25, 25-29,40-49, 60+, etc.10.Only categories with two or three statistically significant odds ratios are used.11.Only statistically significant odds ratios are used, and only rows with three or more suchratios are examined. All nonsignificant odds ratios are ignored. Here, p < .15 is used for thesignificance level. The test values for determining significance were computed, followingGoodman's (10) procedure when one knows how many ratios are of interest. For each table,n 2 - n ratios were computed for off-diagonal cells. Actually, only (n - 1)2 of them arenonredundant.12.The 1973 reference used the same Detroit data set as this analysis.13.These global probabilities would be limited by the marginals: no more choices can beexpected than are found in the minimum marginal cell, F .j or F.

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the structure of adult friendship choices

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