Dr. Bottlender and colleagues also present a new analysis in their letter; the data appear to come from an extension of a previous study (Bottlender and Möller, 2000; Bottlender et al., Eur Psychiatry, in press). Unfortunately, this analysis does not provide more information on the summer birth effect. First, the study group does not appear to be population based (Bottlender and Möller, 2000), so it is not appropriate for discussion of this epidemiological issue. Second, their statement that "it can be assumed that most patients with a residual type of schizophrenia…would also fulfill the criteria for a deficit syndrome" (Bottlender and Möller) is puzzling, as their own data demonstrate that such is not the case. When they state that "50% of the patients had a deficit syndrome according to the criteria proposed by Dr. Kirkpatrick et al.," it is not clear whether they are referring to use of the Schedule for the Deficit Syndrome (1) or the Proxy for the Deficit Syndrome (2). In either case, the 50% prevalence of deficit schizophrenia makes it clear that their deficit and nondeficit groups did not resemble those in previous studies of deficit schizophrenia and summer birth, as the prevalence of the deficit group is about 20%–25% among study groups with chronic schizophrenia and 15%–20% in first-episode, population-based samples (3, unpublished report by E. Messias et al.). As a consequence, there are many false positive diagnoses of deficit schizophrenia in their study. There may be many false negative diagnoses as well, but the information needed to make that judgment is not available to us, as we were not provided with clinical and demographic comparisons of the deficit and nondeficit groups. The appropriate use of the Proxy for the Deficit Syndrome, and especially validity testing for groups defined by it, have been described previously (2, 4–8, unpublished report by Messias et al.).