Of the potential cases and controls who were alive and contactable, refusal rates were higher for cases than for controls (46.7% versus 41.7%). However, these proportions compare favorably with modern refusal rates in epidemiology (59% for cross-sectional and 44% for case-control studies), 87,88 and in a recent large Norwegian longitudinal study (58%). 89 For cases, comorbidity with drug/alcohol abuse or dependence did not predict participation nor did any subtype of schizophrenia (e.g., paranoid or disorganized types). The sample was approximately representative of the Swedish populace in regard to county of birth (Supplemental Figure 4).
