There are limitations to the present study. Although a full intent-to-treat analysis was used, there was a fair amount of missing data at follow-up. Severe substance abusing populations can be difficult to track through follow-up, and ethical restrictions can amplify this effect (e.g., 57% of participants were involved in legal processes, but the institutional review board prohibited contact if they were placed in prison). It is also difficult to characterize TAU in a residential program because of the amount and complexity of treatment received. The ACT intervention could have produced effects that were due to the addition of attention from providers outside the unit or unusually skilled therapists. Our measure of shame was limited to the ISS, but it has not yet been agreed upon how to accurately measure situational levels of shame or distinguish it from guilt, an emotion that has more generally been found to be adaptive (Tangney & Dearing, 2002). Thus, improvements related to shame may have also been connected to changes in guilt. The comparability of this sample to others is unclear, as data were not
