Fourth, the twin studies that we examined used two quite different methods of ascertainment and assessment. One set of studies assessed AUDs via personal interviews, which require subjects to both cooperate and accurately report their AUD symptoms. Another set of studies used registry information, which may be less sensitive but eliminates problems of cooperation and selective recall. Thus, there is considerable heterogeneity in the diagnostic assessments of AUD. In neither the genetic nor the common environmental variance components did the method of assessment induce heterogeneity in the parameter estimates. Accordingly, we can conclude that the method of assessment does not significantly affect estimates of the genetic or common environmental variance components.
