The risk of disease in relatives of a proband with disease was compared to the risk among relatives of 5 unaffected subjects matched by gender and year of birth for each member in the pair (for adoptive relationships the subjects were matched using 5 year age-band intervals). In order to allow equal follow-up time, we additionally required that the relatives of probands and controls were alive and had not been admitted to psychiatric care in Sweden by the date the proband was first hospitalized. The data were analyzed in a conditional logistic regression model using the PROC TPHREG procedure in SAS version 9.1.323. As several possibly correlated pairs of relatives from each family could be included in an analysis, a robust sandwich estimator was used to adjust for the correlated data when calculating the confidence intervals.
