These results should be interpreted in the context of four potentially important methodological limitations. First, we detected subjects with DA from medical, legal and mortality records, a method that does not rely on accurate respondent recall. However, such data likely contains both false negative and false positive diagnoses, the frequency of which we cannot estimate. An epidemiological study of DA conducted in neighboring Norway, which has similar rates of drug use and abuse (Hibell et al., 2007; Kraus et al., 2003), found lifetime prevalence rates of DSM-III-R (American Psychiatric Association, 1987) DA quite similar to those found using our registry based methods (Kringlen et al., 2001). Thus, under-ascertainment of at least the more severe forms of DA is unlikely.
