From the Division of Epidemiology and Community Health, University of Minnesota, Minneapolis, MN.
Received for publication June 7, 2004; accepted for publication October 14, 2004.
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ABSTRACT |
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history; knowledge
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INTRODUCTION |
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Presumably, one kind of useful empirical information is data on the contemporary epistemological foundations of the discipline. Citation analyses are helpful in this regard. By tabulating and categorizing citations, one may document a disciplines institutional or virtual knowledge and perhaps delineate communication networks within and across disciplines (18). Citation analyses also reveal aspects of intellectual history and so help identify not only a disciplines "normal science" (19, 20) but emergent paradigmatic shifts.
Two previous citation analyses have been published in (and on) this journal (21, 22). Both were focused on the use of clinical medicine by epidemiologists and the use of epidemiologic research by clinicians; extensive and growing interactions were found. Other analyses have examined trends in article content, such as the use of race and class (2326).
No such study has systematically considered epidemiologys reliance on statistical or social science research. This is surprising since (bio)statistics is such an important part of epidemiologic training and activity, epidemiology and social science share a common origin, and there is growing interest in social epidemiology (2729).
This paper aims to contribute empirical information on the contemporary epistemological foundations of epidemiology. According to Mertons paraphrase of Newton (30), on whose shoulders do epidemiologists stand? That is, what works do American Journal of Epidemiology (AJE) authors rely on to support, inform, and frame their research, and to what extent do AJE authors use social scientific and statistical citations? This paper does not address the extent to which AJE or other epidemiologic research is used elsewhere. Special attention is paid to statistics, because it is a tool for epidemiologic inquiry and so is a useful guidepost against which to consider social science. Social science is considered because of its prominent role in the ongoing discussion and debates, and because there is little empirical evidence of its influence.
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MATERIALS AND METHODS |
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To compare citation rates across disciplines, I mapped journals perceived to be "leading disciplinary journals" into four groups: 1) epidemiologic journals, 2) medical journals, 3) statistical and biostatistical (referred to here as "statistics") journals, and 4) social scientific journals (table 3). All other citations, including hybrid or interdisciplinary journals such as the American Journal of Public Health and Social Science & Medicine, were coded into an "all others" group. Because there is no established function that maps journals and texts to disciplines, the taxonomy used in this paper is subjective. As in previous research (24), I endeavored to enhance reliability by polling colleagues in many disciplines and letting my groups reflect consensus opinion. This approach appears superior to reliance on existing journal-type codes, which appear too broad for the purposes here (21). To assess sensitivity, I defined extremely inclusive groupings for both the social scientific and statistical citations. Among others, the American Journal of Public Health was added to the epidemiology journal group; Social Science & Medicine, law journals, and social theory text citations were included in the social science group; and the oft cited statistical software reference manual and textbook citations were added to the statistical group. Substantive findings were little changed.
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RESULTS |
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Table 1 presents the 10 most frequent citations in AJE during the study period. Breslow and Days classic text is ranked first. Of note is that all but one of these 10 citations are statistical in nature; in fact, all but two of the top 25 citations are statistical.
Table 2 lists the 25 most frequently cited journals during the study period, the leading two being AJE and the Journal of the American Medical Association (JAMA). Together, the 25 journals account for 38.77 percent of citations. Although classification is difficult, around one third to one half of these 25 journals are medically focused, two are statistical, and none come from the social sciences.
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The remaining citations comprise numerous texts and handsful of citations to (nonleading) medical, public health, psychology, and natural science journals. The median number of times any of these "other" citations were cited is unity.
What about citation trends over the study period? Taken together, the top 10 most frequently cited works show a generally decreasing citation frequency after the late 1980s, which is understandable given the lagged nature of citations. Individually, the top 10 citations show the same general decline with the exceptions of Coxs paper and Rothmans text, which continue their strong influence. In terms of journal groups, figure 1 plots group trends. There are a slight but noticeable decline in the proportion of medical journal citations and a slight increase in the proportion of epidemiologic journal citations over time. There was no obvious reason for the 1983 dip in medical citations; it does not appear to be a data-processing error. Statistical and social science journal citations were fairly constant.
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DISCUSSION |
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AJE authors rely on other AJE articles about 9 percent of the time (table 2), which is almost three times greater than the next most cited journal. This is not surprising for a leading journal in good health. Somewhat surprising is that the frequency has not changed appreciably since Dannenbergs analysis of 19741982 data (21); his data showed a 9.5 percent citation rate, while mine show a 9.33 percent rate. With respect to the most cited journals, my table 2 rankings differ only slightly from Hasbrouck et al.s table 2 (22) because I excluded nonarticle citations, as discussed above.
Although my taxonomy may be debated, it seems clear that articles published in AJE rely equally on medical and epidemiologic research. While reliance on statistical journals is only about 3 percent, the most frequent citations are statistical in nature, and there are high percentages of statistical texts cited (texts are not included in journal groups). While the discipline of statistics clearly matters to epidemiology, social science is another story. I expected low citation rates but was surprised by just how low they were. Again, even an extremely inclusive definition of social science research revealed only slightly larger percentages.
Trend analysis showed remarkably consistent rates. That AJE authors are increasingly relying on epidemiologic instead of medical citations (at least as defined here) bodes well, I think, for the health of AJE as a journal and epidemiology as a discipline.
It is worth emphasizing that, except for table 1, my analyses rely on pooled data. This approach is consistent with past efforts and answers the question at hand. However, additional insight may be gained by collapsing the data to the citing AJE article (i.e., the index article) level and examining the percentage of index articles that cited research in at least one social science, statistical, medical, and epidemiologic journal within my taxonomy. Results show that 100 percent of index articles cite at least one epidemiologic journal article; 84.34 percent cite at least one medical journal article; 41.82 percent cite at least one statistics journal article; and 3.04 percent cite at least one social science journal article. No trends are apparent. Thus, the upshot of this alternative analysis is consistent with the main results.
It is worth repeating that the chief limitation of this paper is my journal taxonomy. Journal groups were subjectively defined, and other groupings might yield different resultsthough I doubt very different. Since many important epidemiologic studies are published in JAMA and other prestigious "medical journals" and since AJE often publishes important statistical papers, such as those by Greenland and Miettinen, classifying journals into groups is challenging.
Nevertheless, the results beg the question of why epidemiologists do not cite more social science articles. Could it be that social science has nothing to offer epidemiology? Or, are epidemiologists not aware of useful social science? Unfortunately, the reasons why scientists cite this or that work are complicated (3436). If presented with these results, philosophers of science might wonder if epidemiology and social science are incommensurable. This is a term used by Kuhn (19) to convey a sense of differing disciplinary paradigms, the upshot of which is that disciplines talk past, instead of with, each other (37). Yet, as demonstrated by the rise of molecular biology, commensurability has little to do with goals and objectives (i.e., dependent variables) and everything to do with 1) language and vocabulary and 2) standards of evidence for explanations. That social science aims to explain the social system and epidemiology aims to explain population health is thus not the problem. Further, my sense is that standards of evidence are not all that different, especially among the leading journals, and that the vocabulary is similar enough.
The social science citation rate appears to defy the facts that epidemiology is a population science and that exposures are not random but socially mediated, an issue recognized not only in the ongoing debate but also by the first epidemiologists, such as Virchow, whose slogan was "Medicine is a social science and politics nothing but medicine on a grand scale" (Virchow cited in Baldwin (38, p. 13)) (4, 10, 39). Extrapolation is always dangerous, but it seems that many epidemiologists envisage their subjects to be Robinson Crusoe, someone affected only by biologic organisms and Mother Nature, not by other individuals or strategic interaction. Even the recent efforts of social epidemiologists seem to treat "society" and "social structure" as island weather, influential but not something to be explained. I believe it is the absence of social science research, especially political economy, that explains the lack of a policy mandate Samet (9) and others seek.
Putting speculation properly aside, this paper shows that AJE authors consistently stand on the shoulders of other epidemiologists, clinicians, and the tools offered by statisticians; epidemiologists do not rely on social science. Just how far epidemiologists can, or will, see and do from this perch remains an issue for discussion.
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NOTES |
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REFERENCES |
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