For the adolescent/young adult lifetime CD symptoms score, data were drawn from wave 1. The majority of subjects were assessed using DSM IV criteria but a small proportion were assessed using DSM IIIR criteria. Sum symptom counts for CD were standardized based on the distribution of symptoms in the CADD community sample. A linear regression was performed using Statistical Analysis System (SAS) 9.3 software (SAS Institute Inc., Cary, NC) to determine residuals from sex, age, and age squared. The coefficients from the CADD community sample were applied to the CADD clinical sample (i.e. Z scores of clinical subjects were expressed as deviations from the means of the community samples). In this case, clinical subjects assessed using DSM IV criteria were standardized to the community subjects assessed with DSM IV criteria, and the same procedure was used for subjects assessed with DSM IIIR criteria. After standardization, only phenotypic data from subjects between the ages of 10 and 25 were included in the analysis. The analysis was performed on 1,789 subjects and run as described in a later section.
