GST, a genetic statistic describing differentiation of populations, has frequently been compared with Hamrick and Godt's (1989) review of the plant literature. We show here that some comparisons may be inappropriate if GST was calculated in a different way than that used by Hamrick and Godt (HG). The alternative method of Nei (1973) is mathematically different from the HG technique, occasionally resulting in different GST values. We reviewed 695 studies that appeared between 1990 and September, 1999 that cited Hamrick and Godt (1989), and found that many of these calculated GST according to Nei's method (46%), with the majority of these papers (61%) including comparisons to Hamrick and Godt's review. We suggest that if GST estimates are compared across studies, it is most appropriate to calculate them the same way. We found that in most cases the magnitude of difference in GST values was small, suggesting that qualitative comparisons of GST estimates between studies are still probably valid. Nevertheless, we identified theoretical and empirical situations in which large differences in GST values are likely to arise. Thus, we advise investigators to carefully consider which method to use in calculating GST for a given data set.

Key words: genetic substructure, GST, population differentiation