Income received during treatment does not affect response to contingency management treatments in cocaine-dependent outpatients

Abstract

Background: Prior studies find no effect of baseline income on response to contingency management (CM) interventions. However, income among substance disordered patients is variable, particularly at treatment entry. This study investigated the impact of during-treatment income, a more proximal estimate of economic resources at the time that CM is in effect, on response to standard treatment or the standard treatment plus CM.

Method: These secondary analyses included 418 cocaine dependent participants initiating community intensive outpatient treatment. We examined whether differences were present in pretreatment and during-treatment overall income, as well as specific income sources. We then conducted a series of regression models to investigate the impact of during-treatment income on treatment outcome.

Results: Participants' during-treatment income was significantly lower compared to pretreatment income, and this difference was largely attributable to decreases in earned income, illegal income, and support from friends and family. Neither the main effect of income, nor the interaction of income and treatment condition, was significantly associated with treatment outcome. CM, however, was a significant predictor of improved treatment outcome relative to standard treatment. Income sources and some demographic characteristics were also significant predictors of outcomes; public assistance income was associated with improved outcomes and illegal income was associated with poorer outcomes.

Conclusions: These results suggest that substance abusers benefit from CM regardless of their income level, and these data add to the growing literature supporting the generalizability of CM across a variety of patient characteristics.

Keywords: Contingency management; Income; Patient characteristics; Socio-economic status; Substance abuse treatment; Treatment outcome.

Figure 1

Predicted longest durations of abstinence (LDA; weeks) for selected income values for participants randomized to standard treatment (ST) or contingency management (CM) conditions. No significant effect of income on treatment outcome is present. The income estimate includes all sources of income (e.g., earned, public assistance, illegal) during the 12-week treatment period. Predicted values were calculated using Model 1 coefficients. Model 1 included the primary variables of interest: treatment condition (CM versus standard treatment), mean centered during-treatment income, and the interaction of these terms.