The current study demonstrates two things: (i) that pay improves workplace attendance of homeless alcohol-dependent adults, and (ii) that making access to the workplace contingent on negative breathalyzer results improves alcohol abstinence without reducing workplace attendance. It is perhaps not surprising that pay improves workplace attendance, but the observation that requiring abstinence as a daily precondition to workplace access significantly improves abstinence without decreasing attendance is a new finding that has important implications for how contingency management procedures can be clinically implemented to improve alcohol treatment outcomes. The homeless adults in this study faced many barriers to overcoming their alcohol dependence. Participants were undereducated, and the vast majority was usually unemployed for 3 years prior to intake. Housing instability was a serious issue, with a large majority spending at least one day in the past 30 outdoors, in a vehicle or in an abandoned house, and 30–40% spending at least one day in a hospital. Many also lacked social support, and only one participant out of 124 was married. In addition, concurrent cocaine or opioid dependence was a common problem. These data suggest a treatment approach that addresses multiple barriers simultaneously could be useful for this population. The current study demonstrated that providing vouchers contingent upon job skills training attendance can increase attendance, and vouchers contingent on alcohol abstinence can promote abstinence from alcohol.
While the Contingent Paid group had less verified and reported alcohol use than the Paid group on a number of measures, the Unpaid group had an intermediate level of use that was not statistically more than the Contingent Paid group in any of the analyses of the raw data without covariates included in the analysis. The relatively low level of verified and reported alcohol use in the Unpaid group was in no instance statistically less than the Paid group, but warrants discussion due to the similar level of abstinence in absolute terms as the Contingent Paid group. The similar levels of abstinence in the Contingent Paid and Unpaid groups may have been an artifact of the collection rate of random breath samples, as the Unpaid group had the lowest collection rate. It seems plausible that missing samples would be more likely to be positive than successfully collected samples (an assumption that is the basis of MP analyses), raising the possibility that measured alcohol use in the Unpaid group was artificially low due to the higher rate of uncollected samples. Second, one of the variables on which the groups were stratified was the number of self-reported days out of 30 preceding intake with any level of drinking. The average number of drinks per day was not a stratification variable, however, and the Unpaid group had a lower number of reported drinks per day at intake, a difference that approached statistical significance (P
= 0.08; Table ). Amount of alcohol consumption has consistently predicted poorer treatment outcomes across a range of alcohol treatment methodologies, with no known report showing the opposite association (e.g. Solomon and Annis, 1990
; Duckert, 1993
; Sobell et al., 1995
; Kavanagh et al., 1996
; Breslin et al., 1997
; Kranzler et al., 1999
; Greenfield et al., 2002
; Haver, 2003
; Staines et al., 2003
). It is possible that the relatively low level of measured alcohol use in the Unpaid group was partially due to these factors, a supposition that is supported by the estimated marginal means displayed in Supplementary Table S1
. Accounting for collection rate (random samples only) and drinks per day at intake increased the level of positive breath samples in the Unpaid group relative to the Contingent Paid group for both random and monthly breath samples, as evidenced by the estimated marginal means displayed in Table and Supplementary Table S1
A factor that complicated the execution of the current experiment was the collection procedure for the random breath samples. Due to the relatively rapid elimination rate of alcohol, standard breath analyses require frequent testing to obtain an accurate representation of alcohol use. Across the three groups, the collection rate of the random samples in this study was ~60%. In addition, no random breath samples were collected before 9 a.m. or after 5 p.m., leaving open the possibility that much alcohol use was not captured by these assessments. These factors might contribute to artificially low measured rates of alcohol use, and explain why rates of self-reported heavy drinking were typically higher than rates of positive breath samples. These limitations do not necessarily eliminate the possibility of using contingency management interventions for alcohol use, however. Other biological assays that have a longer detection window could be used, as could measurement techniques that reduce the costs associated with the random assessment procedure in the current experiment. For example, internet-based verification techniques have been developed for measuring carbon monoxide levels for smoking behavior (Dallery et al., 2007
). Similar techniques could allow for obtaining and verifying breath samples remotely, although these techniques would not be practical for homeless populations that lack internet access.
Moving homeless, alcohol-dependent adults out of poverty is a difficult task with many obstacles, but this study suggests two features of treatment programs that could be important when addressing this population. First, payment for attendance in training or assistance programs can significantly increase attendance and utilization of these services. Second, abstinence-contingent access to paid training can significantly increase abstinence from alcohol.