With the exception of this gender modulator, this study was unable to determine the other cause(s) of the high degree of heterogeneity, however, it is possible to speculate on some potential sources. Firstly, four studies did not use standardized methods (DSM-III-R or -IV criteria) for diagnosing opioid dependence.1,2,11,20 For example, the dependence status of Drakenberg and colleagues’ subjects was determined postmortem by examining opiate toxicology, history of opiate abuse, and whether or not physical body-needle tracks were present. This method of assessing opioid dependence has not been formally validated and, furthermore, the authors did not state the specific cut-offs they used for each criterion. Thus, it is impossible to know how the authors decided in borderline situations and, if this may have impacted on results.
