Synchronous versus diachronous methods in the measurement of obsolescence by citation studies

Abstract

Using the literature of human and medical genetics, the results of a synchronous citation study of obsolescence over a 19-year period were compared with the results of a di achronous citation study. If the first two years of synchronous data are excluded, the rate of obsolescence measured synchro nously is statistically equivalent to the rate of obsolescence measured diachronously. The assumption that synchronous studies need to be cor rected to account for the growth of the literature was tested. The data collected support the hypothesis put forward by Brookes that the growth of the literature and the growth of the number of contributors to that literature have opposite effects in the measurement of obsolescence. The results of a synchro nous study corrected for the growth of the literature and also for the growth in number of contributors were statistically equivalent to synchronous data with no corrections whatever.