Data on head injury were obtained primarily from the modified SCID-I, supplemented where available by collateral information from family members and medical records. All subjects were asked whether they had ever had any head injuries and whether they had ever lost consciousness. Loss of consciousness (LOC) was determined to be momentary (ie, dazed, stunned, or unconsciousness for <2 minutes) or longer. Additional questions and collateral information determined the following information with regard to each head injury: age of occurrence, circumstances of the injury, and any sequelae, including approximate duration of LOC and treatment received. Three investigators (J.H., E.W.C.C., and A.S.B.) independently rated the occurrence and severity of head injury while masked to the diagnostic group, age at onset, and identifying data. The investigators used the following coding scheme developed for a study of head injury in Alzheimer disease4: 1 indicates no head injury; 2, minor head injury with no LOC and no history of being stunned or dazed; 3, minor head injury with momentary LOC only, or a history of being stunned or dazed; 4, head injury with LOC more than momentary but less than 1 hour, and/or dizziness, confusion, and/or behavioral changes in the days following; 5, head injury with LOC for more than 1 hour but less than 1 day, and/or headaches, dizziness, and/or confusion in the months following; 6, head injury with coma lasting 1 to 4 days; and 7, head injury with coma lasting 5 days or longer. Consensus ratings were used for each subject included in the study, with ratings of 2 or greater indicating the occurrence of a head injury.4 Childhood head injuries were defined as those occurring at or younger than 10 years, consistent with 2 previous studies.6,7 Since the most critical period of neurodevelopment related to risk for schizophrenia is unknown, we also examined head injuries occurring through adolescence, ie, up to and including 17 years of age. In the schizophrenia group, only head injuries occurring before onset of psychosis were considered. Three subjects in the unaffected group and no subject in the schizophrenia group had a history of multiple head injuries; for these subjects, the earliest head injury was used in the analyses.