The authors examined the effects of a collaborative care intervention for anxiety disorders in primary care on lower-income participants relative to those with higher incomes. They hypothesized that lower-income individuals would show less improvement or improve at a lower rate, given that they would experience greater economic stress over the treatment course. An alternative hypothesis was that lower-income participants would improve at a higher rate because the intervention facilitates access to evidence-based treatment, which typically is less available to persons with lower incomes.
Baseline demographic and clinical characteristics of patients with lower (N=287) and higher (N=717) income were compared using t tests and chi-square tests for continuous and categorical variables, respectively. For the longitudinal analysis of intervention effects by income group, the outcome measures were jointly modeled at baseline and at 6, 12, and 18 months by study site, income, time, intervention, time and intervention, income and time, income and intervention, and time, intervention, and income.
Although lower-income participants were more ill and had greater disability at baseline than those with higher incomes, the two income groups were similar in clinical response. The lower-income participants experienced a comparable degree of clinical improvement, despite receiving fewer treatment sessions, less relapse prevention, and less continuous care.
These findings contribute to the ongoing discussion as to whether or not, and to what extent, quality improvement interventions work equally well across income groups or require tailoring for specific vulnerable populations.