To the Editor: It is difficult to know how to respond to the comments of Dr. Crow. Our object was not to torture the data but to present them so that readers could see the field for what it is—contradictory—and then to dissect the evidence and expose any truth within it. We were not searching for positive findings. Indeed, we would have been pleased had there been a definitive negative result, something that the correspondent appears to see clearly, despite a lack of evidence. At no stage did we suggest that a causal relationship has been established for any one obstetric risk factor. That would have been foolhardy.

We do not understand the objection to grouping risk factors into categories that may share the same underlying mechanism. This is a well-recognized and useful practice found even in the correspondent’s own research R1605CIHBGEDJ, R1605CIHBBHEC. Neither do we understand the objection to the concept of multiple risk factors. Current understanding of causal mechanisms precludes the view that there is a single causal factor for any complex disorder. The concept of multiple risk factors for schizophrenia obviously applies to the genome R1605CIHJCIIA. Why not to the "envirome" as well?