A total of 86 individuals were eligible and agreed to participate in the study. Of these, 66 completed the 4-week baseline assessment with less than 80% adherence to their key anti-retroviral medication. Randomization assigned 34 participants to voucher incentives and 32 to the comparison group. At intake, participants had a mean CD4 count of 300 and a median viral load of less than 75 copies/mL. Half had viral levels below the limit of quantifiable detection. Two participants died during the intervention period; their data are included in the analysis. Characteristics of study participants are given in .
Means (and standard deviation) of baseline characteristics of study participants by treatment group
3.1 Unit costs
Screening during the 4-week baseline observation period cost $42.53 per patient, including the evaluation of participant eligibility, identification of the medication to monitor, and monitoring. Of 103 individuals screened, 86 underwent baseline evaluation and 66 were randomized. Thus for each patient randomized, another 0.56 patients were screened who were too adherent to justify intervention or dropped out before randomization. We assigned a screening cost of $66.37 ($66.37=1.56 × $42.53) to those randomized to the voucher group.
We estimated that medication management visits cost $44.71. This included the time of the medication coach counseling the patient and documenting care. Also included was the cost of time that research assistants spent on visit reminders, maintaining the medication log, downloading the monitoring cap, and preparing an adherence report for the medication coach. The electronic monitoring cap and medication reminder timer cost $95 per patient.
Participants were scheduled for voucher visits twice each week. These visits cost $8.50 each. This represents the cost of visit reminders, downloading data from the electronic cap on the medication vial, calculating voucher incentive earnings, and dispensing vouchers.
We estimated the cost of administering the voucher program by the study manager. The average administrative cost was $135 per week. We estimated that $123 of vouchers were issued each week during the peak of study activity. For every dollar cost of the voucher, there was an additional $1.10 in administrative cost ($1.10=135/123).
3.2 Cost and utilization
Health care utilization is presented in . During the 12-week intervention period, the voucher group obtained an average 5.5 coaching visits and the comparison group 5.0 visits, a difference that was not statistically significant.
Mean (standard deviation) of health care utilization by treatment group and study phase
Mean health care cost per participant are presented in . The voucher intervention cost an average of $942. This cost included the $66 for initial screening, the $378 face value of the vouchers, $416 for vouchers’ administrative cost, and $81 for adherence assessments and follow-up reminders. After screening, the intervention cost an average of $292/month.
Mean (and standard deviation) of health care cost in U.S. dollars by treatment group and study phase
Anti-retroviral drugs prescribed to the voucher group cost $2,572 during the 12-week intervention period. This was significantly greater than the $1,973 in anti-retroviral costs incurred by the comparison group (p<.01).
The voucher group incurred a mean of $1,871 in medical care costs, compared to a mean of $3,099 incurred during the intervention period by the comparison group. This difference was not statistically significant. One member of the comparison group was hospitalized for 16 days, at a cost of $48,595. With this outlier excluded, the comparison group incurred a mean of $2,688 in medical care costs.
During the intervention period, the voucher group incurred significantly more total cost, including the cost of intervention, coaching, medical care, and HAART pharmacy (p<.01).
During the 4 week follow-up period, the groups had no significant differences in health care utilization. The voucher group had higher substance abuse treatment costs (p<.05) and higher total costs during the follow-up period (p<.05).
During the entire 16 weeks after randomization, the voucher group incurred a significantly higher cost for anti-retroviral therapy (p<.05) and a significantly higher total health care cost (p<.05).
3.3 Adherence and Outcomes
Outcomes are reported in . Participants randomized to incentive vouchers were significantly more adherent during the 12-week intervention period, as determined by self-report, pill count, and on-time opening of the medication monitoring bottle. On-time openings were 78% in the voucher group, and 56% in the comparison group (p<.001). The voucher group had increased its on-time openings from 50% at baseline. The comparison group had 52% on-time openings at baseline.
Mean (standard deviation) of outcomes by treatment group and study phase
During the 4 week post-intervention monitoring period, adherence by electronic monitoring fell to 66% in the voucher group, which was not significantly greater than the 53% adherence rate in the comparison group (p=.07). There were no significant differences between treatment groups in HIV-1 RNA levels, CD4 counts, or health status as measured by SF-36 at any point in time.