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Median age difference (D) is obtained by subtracting the median value of the age distribution of the references in a scientific paper from the citing half life of the journal in which it is published. As an indicator of the state of knowledge of research groups presents some interesting properties: 1) it can be related with the incorporation of information pieces in an informal way, say the rate of self-citations; it can follow the natural tendency of the groups towards a progressively updated state of knowledge, and more productive groups will tend to use more recent information. These natural hypotheses are investigated using as a case study of a medium sized Spanish institution engaged in food research. The institution scientific output comprised 439 papers published between 1999 and 2004 in SCI journals from 16 research teams. This paper analyzes teir 14,617 references. The variables studied are number of each group’s published papers, number of authors per paper, number of references per paper, type of documents cited, self citation rate and chronological range of the citations. Number of authors per paper ranged between 1 and 15. The most frequent value (N = 128) is 3 authors. Average number of authors per paper is 4,03 (SD = 1,74). Mean number of references per paper (including review papers) is 33,3 (SD= 17,39) with slightly differences between the groups. Mean self citation rate is 13.72 % (SD = 11,7). The biggest chronological range is 119 years; half of all ranges are 30 years and the general mean for this variable is 33.34 years (SD = 16.34). D values are associated with self-citation rate and we found a negative relationship between D and chronological range of references. However, the correlation figures were too small to reach any sound conclusions about the effect of these variables. Number of references per paper, number of contributing authors and number of papers published by each team were not associated with D. D values can discriminate between advanced groups working with updated information and other delayed research teams. Publication delay affects D figures. Discontinuity of research lines, heterogeneity of research fields and the short time lapse studied could have some influence on the results of this study. It is suggested that wider coverage is needed to properly evaluate the use of D values as indicators of information update of research groups. |
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