We examined the effect of voucher incentives on participation in telephone continuing care for cocaine dependence. Our primary finding was that providing patients with incentives for completing continuing care sessions dramatically increased the number of sessions attended in the first year of the protocol. Among all patients randomized to the non-incentive condition, the average number of completed sessions was 7.2. Among all patients randomized to receive incentives, the average number of completed sessions was 15.5. Incentivized patients who completed the continuing care orientation completed 67% of possible continuing care sessions, as compared to 39% of non-incentivized patients who completed orientation. An attendance rate approaching 70% of possible continuing care sessions over a 12 month continuing care protocol is very unusual (McKay, 2009a
It is also unusual to achieve such a large effect of voucher incentives on attendance. Prior randomized clinical trials of voucher incentives for attendance have yielded, in general, small effect sizes (Lussier et al., 2006
), and it was possible that the delay in reinforcement necessitated by telephone contact would attenuate vouchers’ reinforcing effect. Perhaps the relatively low threshold for treatment engagement allowed the incentives to exert a greater influence than they might have in the context of more intensive or less flexible outpatient continuing care.
Among all participants assigned to receive incentives, the average voucher earnings were about $200, and the voucher cost of each additional session in TMAC+ relative to TMAC was about $23.00. Previous voucher protocols for treatment attendance have varied widely in reward magnitude, and none have extended past 12 weeks, hindering direct comparison. A cost-effectiveness analysis planned upon completion of the study will place the cost of the protocol in context of the benefits, if any, achieved by additional treatment participation.
Despite the large effect of incentives on treatment utilization, the difference in treatment entry rates between TMAC and TMAC+ did not reach significance, and 18% of those who were eligible for incentives declined to enter study treatment, despite substantial outreach efforts by clinical staff. Perhaps providing an incentive for completing orientation would have further increased TMAC+ treatment entry.
In both conditions, most participants made some of their “calls” in person. At a minimum, many participants may have occasionally combined their treatment contacts with their quarterly research evaluations or, for TMAC+ participants, their trips to the office to pick up their rewards. Some TMAC+ participants completed all their sessions by phone, even when their counselors were available to see them in person, so it is clear that telephone contact is a preferred treatment modality for some individuals. It is not clear the extent to which offering participants a choice of modality may have boosted participation relative to offering the program by telephone only.
About 10% of patients earned more than the planned maximum number of vouchers through participation in step-up care. This suggests that the adaptive protocol successfully provided additional sessions to patients at higher risk. However, it also raises the concern that patients had an incentive to do poorly or to stay in TMAC+ rather than accept referrals to a higher level of care. This suggests a need to monitor incentive protocols closely and to consider a firm limit on rewards.
As an effectiveness study, the clinical trial from which these data are drawn was designed to test a “real-world” application of efficacious treatment. Therefore, our participants are broadly representative of those entering publicly-funded IOP for cocaine dependence in a northeastern US city, and our results can be expected to generalize to similar patients and settings. However, there are some limitations to the generalizability of our findings. Most of our participants were unemployed at study entry, and fewer than half reported having worked regularly over the prior three years. It is possible that employed patients may not respond as well to comparable incentives, or that they, as well as those residing in a larger geographical area, may balk at picking up incentives in person during business hours.
An additional limitation of the present analysis is that it examines only participants’ first year of treatment participation, during which TMAC+ participants were eligible to receive incentives. It is not yet known whether TMAC+ participants’ high rate of participation continued in the absence of incentives. Finally, it remains to be seen whether increased treatment participation among TMAC+ participants yields improved treatment outcome.