M E A N R E S P O N S E T I M E - A N E W I N D I C A T O R

O F J O U R N A L C I T A T I O N S P E E D W I T H A P P L I C A T I O N

T O P H Y S I C S J O U R N A L S

A. Schube r t , W. G1/inzel

Information Science and Seientometrics Research Unit, Librw'y of the Hun•arian Academy of Sciences, P.O. Box 7, 1361 Budapest, Hungary

A new measure of the citation speed of journals is proposed. The indicator is based on the response time, i.e., the time elapsed between the publication date and the date of the first citation of a paper. Indicator values of 109 physics j ournals are presented.

1. I N T R O D U C T I O N

Citation indicators are extremely versatile tools in evaluating science journals [1]. They have been used to assess, among others, the impact and the immediacy [2], the influence [3] and the usefulness [4] of journals as well as to find their place in the information network of a particular subject field [5]. Ail these indicators have been successfully used in the field (or in specific sub- fields) of physics [3--20].

Beyond the "snapshots" provided by the indicators based on one-year citation counts, indi- cators characterizing the temporal behaviour of the citation process are of particular interest [19]. The speed at which the scientific community reacts to a publication might influence crucially the rate of a research project through the so called "cumulative advantage" or "success-breads- success" mechanism [21].

The only indicator so far used to assess citation speed is Garfield's immediacy index [2]. By definition, "the 1979 immediacy index would be calculated by dividing the number of all journals ' 1979 citations of items published in 1979 by the total number of source items it published in 1979" [2]. Although the immediacy index is claimed to be a "measure of how quickly the 'average cited article' in a particular journal is cited" [2], the following reservations are to be ruade.

1. The immediacy index superimposes citation rate and citation speed. Since citation rates largely depend on the science fields, the language of publication, etc., it may well happen that a relatively slow journal of a highly cited area surpasses in immediacy index the fastest journal of a sparsely cited field.

2. A great majority of science journals does not receive at ail a sensible amount of citations in the year of publication because of publication delays, distributional difficulties, etc. Although such journals may meet with justifiable disapproval, an indicator should be able to differentiate among the citation speed of such journals, too.

3. It would be most convenient if an indicator of citation speed had, or at least were related to, the dimension of time.

These points motivated our attempts in finding some alternative measures of citation speed.

2. METHODS

Obviously, an ideal temporal characterization of the citation process would require tracking the full citation "life histories" of each single paper of a particular journal. This procedure carmot be practically accomplished because even in the relatively "fast" fields a citation period of about 10--15 years would be needed to complete a study. In order to reduce the required time and work, vve suggest the following. For each paper of a particular journal the date of its first citation only should be recorded. The time elapsed between the publication and the first citation of the paper wil I be called the response time. The indicator we propose to measure citation speed is the mean response time (MRT), which is a properly formed average (see below) of the response times of ail the papers in a particular journal.

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A. Schubert, IV. Gliinzel: Mean response time . . .

In our experience, it is unlikely that a paper which have not got a single citation in the first four years after publication will get any citations later. Therefore, response time studies can be restricted to a five-year citation period (the year of publication plus four subsequent years). The response time of ail papers having got no citations in this period is to be taken infinite. This, of course, makes simple arithmetic average unsuitable in forming M R T . We suggest, instead, the use of an "exponential average"

= - l n (n -1 ~ e - t ' ) . i= l

I n particular,

M R T = - I n ( f 0 + f t e -1 + f 2 e -2 + f 3 e -3 + f4e -4 ) ,

wheref~ is the fraction of papers receiving their first citation in the i-th year after publication.

3. RESULTS

In figure 1, the response-time distributions and the M R T values of 109 physics journals are presented. Tapes of the Science Citation Index data base of the Institute for Scientific Information, Philadelphia, were used as data source. Source year 1979 and citations in the period 1979--83 were considered. Tbe single journals were identified by their 11 character abbreviation used in the SCI data base. In order to obtain statistically reliable indicator values, only journals with more than 100 source items in 1979 were taken into account. M R T values range between 0.4 (PHYS REV L) and 6"0 (HIGH T E M P R R); as a rule of thumb, journals with M R T value below 1"0 can be regarded as "fast", those above 1.0 as "s low" ones.

Received 24. 6. 1985.

Re f erences

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[10] Singleton A.: J. Docum. 32 (1976) 258--289. [11] Vlach~ J.: Czech. J. Phys. B 2 6 (1976) 1395--1406; B 2 7 (1977) 1417--1424. [12] Cawkell A. E.: J. Am. Soc. Inform. Sci. 29 (1978) 41--46. [13] Vlach3) J.: Europhys. News 9 (1978) 4--5. [14] Vlach3) J.: Czech. J. Phys. B 30 (1980) 239--242; 477--480; B 31 (1981) 351--355. [15] Todorov R.: Scientometrics 5 (1983) 291--301. [16] Midorikawa N.: Scientometrics 5 (1983) 361--374. [17] Vlach3~ J.: Czech. J. Phys. B 3 3 (1983) 585--591; 1173--1176. [18] Todorov R.: Scientometrics 6 (1984) 127--137. [19] Vlach~ J.: Czech. J. Phys. B 34 (1984) 267--270. [20] Vlach3~ J.: Czech. J. Phys. B 35 (1985) 187--190; 473--476; 589--592. [21] Price D. de Solla: J. Am. Soc. Inform. Sci. 27 (1976) 292--306.

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