Few studies examined how the factor structure of substance use or related problems generalizes across differing sampling schemes. In a comparison of substance use behaviors between volunteer and random samples, volunteers reported a greater incidence of psychosocial risk factors (such as lower average socioeconomic status and IQ) and higher rates of SUDs for “hard” drugs, but the two groups were not distinguishable on the basis of overall number or severity of SUDs. Further, volunteers demonstrated less social desirability bias in self-reports. [28] Comparing drug use problems between Swedish heavy drug users and a population sample, a drug problems inventory best fit a three-factor solution among the heavy drug using sample (including substance treatment in-patients and individuals who were either incarcerated or on probation), but a two-factor solution in the population sample. However, the authors of this particular study noted that the low prevalence of substance-related problems in the population sample suggest that factor results may be unreliable in that sample. [29]
