These findings should be considered in light of several limitations, which may impact the generalizability of our conclusions. Neither of these samples were representative of the U.S. population as a whole, and our model does not include the effects of either ethnicity or age, both of which were more diversely represented in our clinically over-selected sample. Previous studies report similar factor structures across ages [21], as well as among African-, European-, and Mexican-American individuals for alcohol [40] and cocaine dependence. [41] Our finding of measurement invariance in substance dependence across samples in the current study, despite these additional potential confounds not being explicitly modeled, strengthens our conclusion, based on this and previous studies, that the factor structure of substance dependence is consistent across samples with varying demographic characteristics.
