Changes in the use of literature with time - obsolescence revisited

Library Trends, Spring, 1993 by Maurice B. Line

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CITATION STUDIES OF OBSOLESCENCE

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One major theme of our earlier article was the distinction between synchronous and diachronous obsolescence and the need to allow for growth of the citable literature in synchronous studies; there had been a very large growth of literature in most subjects, especially the sciences and social sciences. A similar allowance has to be made in diachronous studies for changes in the size of the citing literature. We mentioned a third type of obsolescence, diasynchronous, which uses synchronous studies carried out at different times. As we pointed out, nearly all studies had been based on synchronous data without allowance being made for growth. These issues appeared to arouse particular interest, and several papers attempted to examine them further. It was argued on theoretical grounds that no allowance need be made for synchronous data (Stinson & Lancaster, 1987). Some studies purported to show that there was little or no difference between the results produced by synchronous and diachronous citation studies (Oliver, 1971) while others found that there was a difference (Line & Carter, 1974). Similar differences appeared in library use studies (see later discussion). Different results emerge, not surprisingly, from different data, depending perhaps on the subject or even the journals analyzed--and the period covered (see later discussion).

Motylev (1981) has produced logical proof that the two main types of study are not equivalent. Other articles by him (1976, 1982, 1989) are, like that of Artus, highly critical of statements and assumptions about rapid aging. One of them (1976) concludes that "use frequency can be considered a function of document aging only in an ideal information system" and "information use determined from citations or requests to reference information collections is only a very approximate reflection of document aging" (p. 97). Heisey's (1988) diasynchronous study, which was able to make accurate adjustments for changes in the number of both citable and citing papers, has a particularly useful discussion of the issues. Clark (1976) showed that "theoretically, synchronous and diachronous studies are each a restricted type of the full diasynchronous study, even though, experimentally, a diasynchronous study may consist of a sequence of synchronous ones..." (p. 33). Griffith et al. (1979) pointed out that "the |pure' case, observations of all uses over time of the same items by a single unchanging literature, cannot occur" (p. 180)--both synchronous and diachronous studies are "impure" (which is why correction is needed).

Several articles (e.g., Line & Sandison, 1974; Marton, 1985) have pointed out that there are two periods in the life of an article: an early one, described by some as "immediacy" or "updating," and a "basic" one, extending over the whole life of the article. Barnett et al. (1989), in an article that uses citation data to examine diffusion in all broad subject fields, develop a mathematical model to represent this feature (their paper, incidentally, appears to show unawareness of any information science literature). Partly because of this phenomenon, Egghe and Rao (1992) argue that the obsolescence function is not a constant but merely a function of time, and that this jeopardizes the use of aging factors.

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Changes in the use of literature with time - obsolescence revisited

Library Trends, Spring, 1993 by Maurice B. Line

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