Drs. Maciejewski and Mazure raise two relevant issues about our recent article, in which we attempted to estimate the proportion of the relationship between stressful life events and the onset of major depression that was causal. First, they ask whether the odds ratios (not, as they state, the estimated risk for depression) for the association between stressful life events and major depression were significantly different between the monozygotic twins and the general population. It is not possible to formally test these two odds ratios because they were derived from quite different calculations—the first from a co-twin control analysis of twin pairs and the second from an individual-wise analysis of the entire sample, which included the monozygotic twin pairs. We can, however, compare the standard error of these estimates or, more precisely, of the regression coefficients (bs) from which the odds ratios were calculated. For the monozygotic twins, the b for predicting a depressive onset from the occurrence of a personal stressful life event was 1.28 (SD=0.20), whereas the parallel estimate for the entire sample was 1.73 (SD=0.13). Thus, the standard errors of the regression coefficients were far from overlapping, suggesting that these parameter estimates are meaningfully different.