There are a number of factors that could potentially account for the discrepancies observed between the various reports above and the present study. These include but are not limited to differences in diagnostic criteria for schizophrenia, all cases were adult onset, different time frames of serum collection related to illness onset, differences in laboratory assays, and multiple vs single serum specimens. In addition, our sample was drawn from the military population that differs from the general US population in several important ways. The male to female ratio in the military is much higher than in the general population, making it difficult to achieve adequate power when analyzing females separately. Comprehensive medical screening prior to entry into the military creates a healthy worker effect in the population and skews our sample toward individuals with later onset of schizophrenia. Also, our cases are a convenience sample of individuals with schizophrenia in the military. A small degree of bias introduced by any of these factors could account for the significance and direction of our findings.