Effects of Voucher-Based Intervention on Abstinence and Retention in an Outpatient Treatment for Cocaine Addiction: A Randomized Controlled Trial

Experimental and Clinical Psychopharmacology 2009 American Psychological Association 2009, Vol. 17, No. 3, 131 138 1064-1297/09/$12.00 DOI: 10.1037/a0015963 Effects of Voucher-Based Intervention on Abstinence and Retention in an Outpatient Treatment for Cocaine Addiction: A Randomized Controlled Trial Olaya Garcia-Rodriguez and Roberto Secades-Villa University of Oviedo Stephen T. Higgins University of Vermont Jose R. Fernandez-Hermida, Jose L. Carballo, Jose M. Errasti Perez, and Susana Al-halabi Diaz University of Oviedo The aims of this study were to assess whether voucher magnitude improved cocaine abstinence and retention in an outpatient treatment for cocaine dependence, and to determine the effectiveness of a contingency management intervention in a European cultural context. A randomized controlled trial was conducted in which 96 participants who were randomly assigned to 1 of 3 treatment conditions in a community setting: standard outpatient treatment, community reinforcement approach (CRA) plus low monetary value vouchers (each point earned was equivalent to 0.125, US$ 0.18), and CRA plus high monetary value vouchers (each point was worth 0.25, US$ 0.36). In the standard treatment group, mean percentage of cocaine-negative samples was 88.45%, versus 96.09% in the CRA plus low-vouchers group, and 97.07% in the CRA plus high-vouchers group. Retention rate at 6 months was 36.5% in the standard treatment group, 53.3% in the CRA plus low-vouchers group, and 69.0% in the CRA plus high-vouchers group. The CRA plus vouchers groups obtained better results than the standard program. This study showed that treating cocaine addiction by combining CRA with vouchers was more effective than standard treatment in community outpatient programs in Spain. Keywords: cocaine, community reinforcement approach plus vouchers, reinforcement magnitude, community setting Olaya Garcia-Rodriguez, Roberto Secades-Villa, Jose R. Fernandez-Hermida, Jose L. Carballo, Jose M. Errasti Perez, and Susana Al-halabi Diaz, University of Oviedo; Stephen T. Higgins, University of Vermont. This project was funded by the Spanish National Plan on Drugs (PNsD) (Ref. MSC-06-01) and supported by a predoctoral grant from the University of Oviedo (Ref. UNIOVI-04-BECDOC-05) and a predoctoral grant from the Foundation for the Promotion of Applied Scientific Research and Technology in Asturias (FICYT) (Ref. BP05-002). The authors would like to thank those responsible for the Proyecto Hombre clinics in Asturias and Madrid for their invaluable help. Correspondence concerning this article should be addressed to Olaya Garcia-Rodriguez, Department of Clinical Psychology, University of Barcelona. E-mail: olayagarcia@ub.edu Approximately 12 million Europeans, roughly 4% of all adults, have used cocaine at some time. Around 2 million of these (0.6% of all adults) are classified as current users (European Monitoring Centre for Drugs & Drug Addiction, 2007). Spain reports the highest levels of cocaine use in Europe (more than one fifth of all European cocaine users are in Spain), and for the first time cocaine use levels exceed those reported from the United States (United Nations Office for Drugs & Crime, 2007). In parallel, demand for cocaine treatment is increasing in Spain, and accounts for 40.5% of all drug-related treatment demand. The provision of specialized responses for cocaine users remains limited throughout Europe given that no pharmacological treatment has been found to be reliably effective in the treatment of this population. Therefore, the development and dissemination of effective behavioral and psychosocial treatments for cocaine dependence are important public health priorities in Europe, and especially in Spain. The community reinforcement approach (CRA) plus vouchers intervention was initially developed by Higgins and his colleagues (1991) for the treatment of cocaine addiction in outpatient contexts. The voucher-based incentive approach involves the provision of vouchers exchangeable for goods and services contingent on predetermined therapeutic goals, usually abstinence. Results from a series of randomized clinical trials support the efficacy of this combined intervention approach in the treatment of addiction to different types of drugs and in diverse populations (Lussier, Heil, Mongeon, Badger, & Higgins, 2006; Prendergast, Podus, Finney, Greenwell, & Roll, 2006). Recent years have also seen the development of the adaptation of the CRA plus vouchers for its application by means of new technologies (Bickel, Marsch, Buchhalter, & Badger, 2008). Furthermore, preliminary results from some studies suggest the effectiveness of CRA plus vouchers for retaining outpatients in treatment and achieving cocaine abstinence in a community setting in Spain (Garcia-Rodriguez et al., 2007; Secades-Villa, Garcia-Rodriguez, Higgins, Fernandez-Hermida, & Carballo, 2008). Nevertheless, these Euro- 131

132 GARCIA-RODRIGUEZ ET AL. pean studies are still quite recent, and there is a need for data supporting the generality of the results obtained in the United States. In addition to examining efficacy, some meta-analyses demonstrate the influence of the reinforcement program parameters, such as immediacy of voucher delivery, duration of the voucher-based reinforcement therapy, or reinforcer magnitude, on contingency management (CM) intervention outcomes (Lussier et al., 2006; Prendergast et al., 2006). The use of vouchers with greater monetary value is generally associated with greater drug abstinence (Dallery, Silverman, Chutuape, Bigelow, & Stitzer, 2001; Higgins et al., 2007). Furthermore, there appears to be a directly proportional relationship between reinforcer magnitude and the cost effectiveness of such interventions (Sindelar, Elbel, & Petry, 2007). Reinforcement magnitude affects not only the effectiveness but also the implementation costs of these programs, and hence their potential for introduction in community clinics. Therefore, it is of great interest to corroborate the applicability of these interventions to a different cultural setting by testing one of the most reliable findings from CM literature (the influence of reinforcer magnitude). The goals of the present study were to determine the effects of voucher magnitude on cocaine abstinence and retention in an outpatient treatment for cocaine addiction and to determine the effectiveness of the CRA plus vouchers program (Budney & Higgins, 1998) in a European cultural context and in a community setting. Participants Method Study participants were 96 cocaine-dependent adults seeking outpatient treatment at two outpatient community clinics in Spain (Clinic A and Clinic B). To be included in this randomized controlled trial, individuals had to be at least 18 years of age, meet Diagnostic and Statistical Manual of Mental Disorders (4th ed., text rev.; DSM IV TR; American Psychiatric Association, 2000) criteria for active cocaine dependence, have used cocaine during the previous month, and live sufficiently close to the clinic to allow them attend it 2 or 3 times a week. Patients with serious psychopathological disorders (such as psychosis or dementia) or active opioid dependence were excluded. At both community clinics, the patients selected for the study were assigned at random to the control group (standard outpatient program) or the experimental group (CRA plus vouchers) according to a computer-generated randomization list. Patients assigned to the control group received the same treatment at the two clinics. Patients assigned to the experimental group received the CRA plus vouchers program with a single variant in the incentives program. At Clinic A (CRA plus low vouchers), each point earned by patients was equivalent to 0.125 (US$ 0.18), and at Clinic B (CRA plus high vouchers), each point earned was equivalent to double the value, that is, 0.25 (US$ 0.36). At Clinic B, patients were recruited over a period of 2 years; at Clinic A, the study lasted just 1 year. Seventeen participants were assigned to the standard outpatient program and 15 to CRA plus low vouchers at Clinic A. Thirtyfive participants were assigned to standard treatment and 29 to CRA plus high vouchers at Clinic B. Patients baseline characteristics are shown in Table 1. There were no significant differences between groups, or between clinics, for any baseline characteristics. Given that patients assigned to the two control groups (standard outpatient program) did not differ in any variable, they were considered as a single group; once again, no statistical differences were found in comparisons with the two experimental groups. Intake Process Patients were informed of the treatment intervention characteristics and the schedule of urinalysis monitoring on giving informed consent during the intake phase. They subsequently completed several instruments, including the Michigan Alcoholism Screening Test (Selzer, 1971), the Beck Depression Inventory (Beck, Ward, Mendelson, Mock, & Erbaugh, 1961), the cocaine-dependence criteria of the DSM IV TR, and the European version of the Addiction Severity Index (Kokkevi & Hartgers, 1995). All these instruments were explained to the patient or administered by a trained staff member. The intake process lasted for two or three individual 1-hr sessions. Urinalysis Monitoring Urine specimens were collected in both voucher groups in accordance with the original format of the CRA plus vouchers program (Budney & Higgins, 1998). Specimens were collected 3 times a week from Weeks 1 to 12 and 2 times a week from Weeks 13 to 24. In the standard treatment group, specimens were collected 2 times a week (Monday and Thursday) from Weeks 1 to 24, with no differences between clinics. Specimens were screened on-site for the detection of cocaine use by means of the Quickscreen Test (Eve Layper Company, Madrid, Spain). The Quickscreen test is a chromatographic immunoassay that rapidly detects patients cocaine use. The reagents in this test detect benzoylecgonine (a cocaine metabolite) at a concentration of 300 ng/ml. All specimens were obtained under direct supervision by a same-sex staff member. Participants in all treatment conditions were informed of their urinalysis results immediately after submitting each specimen. Failure to submit a urine specimen as scheduled rendered it cocaine positive if the patient failed to provide some sort of official justification (job related or medical) and failed to attend to the clinic within the following 2 days to submit a specimen. Treatment Interventions The main details of both treatment programs have been described previously (Budney & Higgins, 1998; Secades-Villa et al., 2008), so that we give only give brief descriptions here. Patients in the three groups who reported alcohol problems were offered monitored disulfiram therapy. In total, 36.5% in the standard outpatient program (35.3% at Clinic A and 37.1% at Clinic B), 26.7% in CRA plus low vouchers, and 34.5% in

VOUCHER-BASED INTERVENTION FOR COCAINE ADDICTION 133 Table 1 Participants Characteristics Variable Clinic A (n 17) Standard treatment Clinic B (n 35) Total (n 52) CRA plus vouchers Clinic A (n 15) Clinic B (n 29) Demographics Gender (% male) 88.2 88.6 88.5 100 86.2 Age (years) a 30.1 5.6 27.5 5.9 28.4 5.8 30.8 4.2 29.4 5.3 Education (years) a 9.62 2.3 9.58 2.7 9.6 2.5 11.1 3.5 10.1 2.4 Marital status (% never married) 70.6 71.9 71.4 63.3 60.0 Employed (% full time) b 88.2 62.9 71.2 86.7 72.4 Served time in prison (%) 12.5 16.7 15.2 0 20.7 Cocaine use Intranasal route (%) 93.8 90.9 91.8 100 100 Weekly intake (g) a 6.70 5.3 4.70 3.5 5.41 4.3 4.39 2.6 4.48 3.4 Years of regular cocaine use a 8.7 5.5 6.57 4.6 7.2 5.0 5.7 3.5 5.89 4.0 Years of occasional cocaine use a 4.9 4.8 2.9 2.4 3.6 3.5 4.8 4.0 3.69 3.3 Age first use cocaine (years) a 19.7 6.9 19.1 3.5 19.3 5.0 22.5 4.7 20.4 4.2 Other drug abuse in lifetime (%) c Alcohol 94.1 87.1 91.5 73.3 86.2 Cannabis 68.8 71.1 70.2 57.1 50 Amphetamines 25.0 23.3 23.9 7.7 24.1 MAST score a 6.75 5.7 6.50 4.8 6.59 5.1 5.73 4.3 6.04 4.1 BDI score a 22.58 8.0 17.95 11.0 19.64 10.1 15.07 6.7 14.81 7.2 Addiction severity index composite score a Medical 0.1395 0.19 0.1333 0.20 0.1355 0.19 0.1534 0.20 0.2250 0.27 Employment 0.4582 0.23 0.5074 0.33 0.4899 0.29 0.3509 0.30 0.4566 0.32 Alcohol 0.3692 0.20 0.2699 0.20 0.3044 0.20 0.2937 0.18 0.3182 0.23 Drug 0.1637 0.06 0.1858 0.07 0.1781 0.07 0.2294 0.08 0.2022 0.09 Legal 0.1680 0.26 0.1915 0.23 0.1832 0.24 0.0500 0.14 0.1571 0.21 Family/social 0.3835 0.22 0.4444 0.16 0.4227 0.18 0.4998 0.20 0.3506 0.20 Psychiatric 0.2767 0.18 0.1675 0.17 0.2063 0.18 0.2070 0.25 0.2013 0.24 Note. CRA community reinforcement approach; MAST Michigan Alcoholism Screening Test; BDI Beck Depression Inventory. Means SD. Usual employment pattern in past 3 years. Three or more times per week, binges, or problematic irregular use in which normal activities are compromised. CRA plus high vouchers agreed to use disulfiram. Use of disulfiram between groups and clinics did not differ significantly. Therapists were master s-level psychologists trained in the specific protocols and with extensive experience in the treatment of drug addiction. The same counselors provided both standard and experimental treatment at each clinic. Standard outpatient program. From Weeks 1 to 24, this treatment consisted of 90-min group therapy sessions twice a week, with groups of 10 to 12 people and based on a cognitive behavioral approach. Individual sessions took place to resolve specific problems, but with no fixed frequency. Group sessions focused on six general topics: improving information about drugs, problem-solving training, relapse prevention, vocational guidance, training and leisure activity workshops, and resolution of family and interpersonal conflicts. Participants in this group received no type of incentive in exchange for maintaining abstinence. CRA plus low vouchers. The treatment for both vouchers conditions was manual-guided CRA plus vouchers therapy (Budney & Higgins, 1998), with one difference: Most of the CRA therapy components were applied in group-based sessions of 10 to 12 people. Thus, the CRA was implemented in two 90-min group-based sessions per week and, in case of need, one weekly individual session, from Weeks 1 to 24. Group sessions focused on three general topics: first, drugavoidance skills, where patients were trained in functional analysis to detect antecedents of cocaine use, problem solving (pros and cons of cocaine use and refusal), and drug refusal training; second, lifestyle change components, where patients were counseled to develop new recreational activities and a healthy social network; and third, other substance abuse, where specific interventions were carried out with all those who reported alcohol problems or cannabis use. In each session, those with skills deficits for working toward any treatment objective were given specific skills training. Individual sessions focused on vocational counseling, relationship counseling, and psychiatric problems. The vouchers program was implemented from Weeks 1 to 24 as follows: All specimens collected from Weeks 1 to 12 that tested negative for benzoylecgonine earned points. Points were worth the equivalent of 0.125 (US$ 0.18) each. The first cocaine-negative specimen earned 10 points, with a 5-point increase for each subsequent and consecutive cocaine-negative specimen. For each three consecutive cocaine-negative specimens, patients earned a 40-point bonus. Cocaine-positive specimens or failure to submit a scheduled specimen set the value back to the initial 10 points, but submission of five consecutive cocaine-negative specimens returned the value to its level before the reset. Points could not be lost once earned. During the period from Week 13 to Week 24, a random system was used in which the earning of points for speci-

134 GARCIA-RODRIGUEZ ET AL. mens testing negative for benzoylecgonine was determined by the roll of a dice. If the number on the dice was even, the patient earned points, but not if it was odd. The 5-point increase for each subsequent and consecutive cocaine-negative specimen was maintained in this phase, even if the dice roll was odd, but the 40-point bonus for each three consecutive cocaine-negative specimens was eliminated. Points were exchangeable for vouchers with a variety of uses, including leisure activities; free transport; meals in restaurants; training; purchases in department stores, bookshops, clothes shops, and art shops; free press subscriptions; and beauty services. All of these goods and services were financed through collaborating companies and institutions from the community (Garcia-Rodriguez, Secades-Villa, Higgins, Fernandez-Hermida, & Carballo, 2008). All the incentives selected by the participants had to be approved by the therapist and deemed to be in accordance with individual treatment goals. CRA plus high vouchers. Patients in this group received the same treatment as the CRA plus low-vouchers group, with one difference. In the vouchers program, points were worth the equivalent of 0.25 (US$ 0.36) each exactly double their value in the other vouchers group. Data Analysis Various descriptive and frequency analyses in relation to participants characteristics were carried out. Comparisons between groups and clinics in baseline characteristics and between the two control groups in dependent variables were performed using Student s t test (after Levene s correction for inequality of variance) for continuous variables and the chi-square test for dichotomous variables. A one-way between-groups analysis of variance, with Levene s correction, was conducted to compare treatment conditions in baseline characteristics, as well mean percentage of cocaine-negative specimens, mean duration of continuous cocaine abstinence (based on the maximum period of abstinence during the 6 months of treatment), and mean weeks retained in treatment in each group. Tukey s post hoc comparison was used for comparing the mean of each condition with the mean of every other condition. Treatment comparisons between the percentages of participants who completed 1 to 6 months of treatment and between those who achieved continuous cocaine abstinence during each month of treatment were also performed using chi-square tests. Missing urine samples were considered positive as outlined above (missing positive). Nevertheless, two secondary analyses were conducted, one in which missing samples were considered as simply missing (missing missing), and a second one in which missing samples were interpolated: We considered them positive only if a sample provided before or after the missing sample was positive (missing interpolated). The results of the secondary analyses were basically the same as the results of the primary analysis, and are only presented with regard to the main outcome variable, percentage of cocaine-negative samples. Effect sizes of principal comparisons were calculated using eta square ( 2 ) for analysis of variance and phi ( ) for chisquare tests. It should be borne in mind that values for small, medium, and large effects are not the same for eta square (.01,.06, and.14) and phi (.10,.30, and.50; Cohen, 1988). Confidence level was 95%, and the statistical package used was SPSS-15. Cocaine Abstinence Results As mentioned in the Participants section, patients assigned to the two control groups (standard outpatient program) did not differ in any variable at baseline. For cocaine abstinence outcomes, patients in these control groups did not differ either, so they were also considered as a single group for comparing the standard treatment condition with the high- and low-vouchers conditions. Comparison data from the control groups with regard to this variable are shown in Table 2. Percentage of cocaine-negative samples was selected as the main outcome measure for this variable. Due to the different numbers of urine samples scheduled in the three groups and the fact that continuous abstinence was likely to be influenced by retention differences, we calculated the mean percentage of cocaine-negative specimens for each patient as well as for each treatment condition from missing positive, missing missing, and missing interpolated analyses. Table 3 shows the percentage of cocaine-negative samples for each group. We found statistical differences in mean percentage of negative samples for cocaine use between the standard Table 2 Equivalence in Cocaine Abstinence in Control Group Variable Clinic A (n 17) Clinic B (n 35) Statistic value p Percentage of cocaine-negative samples a 88.91 15.7 88.22 20.0 0.12 b.90 Duration of continuous cocaine abstinence (months) a 2.44 2.2 2.60 2.3 0.23 b.81 Duration of continuous cocaine abstinence (%) 1 month 76.5 77.1 0.00 c.95 2 months 47.1 51.4 0.08 c.76 3 months 41.2 42.9 0.01 c.90 4 months 29.4 31.4 0.02 c.88 5 months 23.5 25.7 0.02 c.86 6 months 17.6 22.9 0.18 c.66 a Means SD. b Student s t test. c 2 (1, N 52) test.

VOUCHER-BASED INTERVENTION FOR COCAINE ADDICTION 135 Table 3 Mean Percentage of Cocaine-Negative Samples and Mean Duration of Continuous Cocaine Abstinence Sample Standard treatment CRA plus low vouchers CRA plus high vouchers F p 2 Mean (SD) missing positive 88.45 (18.5) a 96.09 (5.6) b 97.07 (6.3) b 3.98 0.02 0.08 Mean (SD) missing missing 89.49 (17.5) a 97.15 (4.8) b 97.89 (5.0) b 4.39 0.01 0.09 Mean (SD) missing interpolated 89.09 (17.3) a 96.59 (5.1) b 97.54 (4.8) b 4.49 0.01 0.09 Mean (SD) continuous cocaine abstinence (months) 2.54 (2.2) a 3.53 (2.3) a,b 3.93 (2.0) b 3.87 0.02 0.08 Note. Means in the same row with different subscripts differ significantly at p.05 in the Tukey honestly significant difference comparison. All dfs for F statistics are (2, 93). treatment group and the two vouchers groups. The results of the secondary analyses (missing missing and missing interpolated) were similar to those of the primary analyses. The magnitude of the differences in the means was medium large, according to eta squared. There were relatively few positive specimens across treatment conditions. The percentage of participants in each group never supplying a cocaine-positive sample in a missing-missing analysis was 46.2% in the standard treatment group, 66.7% in the CRA plus low-vouchers group, and 62.1% in the CRA plus high-vouchers group, with no statistical differences between any conditions. Missing urine specimens were very few in each group, and there were no statistically significant differences between either percentage or number of missing samples across control Group A (M 0.29, SD 0.58) and control Group B (M 0.31, SD 0.79), t(50) 0.09, p.92, or across the standard (M 0.31, SD 0.72), low-vouchers (M 0.47, SD 0.99), and high-vouchers (M 0.38, SD 0.82) conditions, F(2, 93) 0.25, p.77. Thus, for continuous cocaine abstinence results, missing specimens scheduled during treatment and after dropout were considered as positive in accordance with the conditions outlined above. Mean duration of continuous cocaine abstinence achieved in each condition can be seen in Table 3. The high-vouchers group and the standard treatment group differed significantly. Effect size ( 2 ) for this variable was also medium large. With regard to the percentage of participants in each treatment condition who achieved durations of continuous cocaine abstinence of 1 6 months or more during the treatment period, percentages in both vouchers groups were consistently higher than those in the standard treatment group. In the CRA plus high-vouchers group, 93.1% of the patients managed to remain abstinent for at least 1 month of the treatment, compared with 86.7% of the CRA plus lowvouchers group and 79.9% of the standard treatment group. Likewise, 72.4% of the CRA plus high-vouchers group patients attained 3-month abstinence, compared with 60.0% of the CRA plus low-vouchers group and 42.3% of the standard treatment group. Finally, 37.9% of the patients in the CRA plus high-vouchers group succeeded in remaining abstinent throughout the 6 months of the treatment, compared with 33.3% from the CRA plus low-vouchers group and 21.2% from the standard treatment group. We found statistical differences between the standard treatment and the CRA plus low-vouchers group in the percentage of patients who achieved durations of continuous cocaine abstinence of 4 months or more, 2 (1, N 67) 4.25, p.03,.25, and between the standard treatment and the CRA plus high-vouchers group in the percentage of patients who achieved durations of continuous cocaine abstinence of 2 months or more, 2 (1, N 81) 8.45, p.01,.32; 3 months or more, 2 (1, N 81) 6.77, p.0,.28; and 4 months or more, 2 (1, N 81) 5.98, p.01, 0.27. Despite the fact that there were no statistically significant differences between the two CRA plus vouchers groups, we observed a clear trend in favor of the group with the larger value vouchers. The phi statistic for these comparisons indicated a medium effect size. The average amount earned in vouchers was 467 355 (US$ 686 521) in the CRA plus low-vouchers condition versus 1,015 605 (US$ 1,492 888) in the CRA plus high-vouchers condition. Treatment Retention Apart from cocaine abstinence, there were no statistical differences between the two control groups (standard treatment) in retention during the 6 months of treatment. Data from both control groups and from the combined control group compared to the vouchers conditions can be seen in Figure 1. Of the CRA plus high-vouchers patients, 96.6% completed the 1st month of treatment, compared with 93.3% of the CRA plus low-vouchers group and 86.5% of the standard treatment patients. These differences were not statistically significant between any of the groups. In the highvouchers condition, 79.3% of the patients completed 3 months of treatment, compared with 66.7% in the lowvouchers condition and 53.8% of standard treatment patients. These differences were statistically significant only between the high-vouchers group and the standard treatment group, 2 (1, N 81) 5.17, p.02,.25. Finally, 69% of the patients in the CRA plus high-vouchers group completed 6 months of treatment, compared with 53.3% of the CRA plus low-vouchers group and 36.5% of the standard treatment patients. These differences were also statistically significant between the high-vouchers group and the standard treatment patients, 2 (1, N 81) 7.84, p.01,.31, as were the retention rates for the 4th, 2 (1, N 81) 6.77, p.01,.28, and 5th months of treatment, 2 (1, N 81) 6.08, p.01,.27. The magnitude of the differences in percentage of patients retained during the treatment was medium, according to the phi statistic.

136 GARCIA-RODRIGUEZ ET AL. 100 80 % par cipants 60 40 20 0 CRA + high vouchers CRA + low vouchers Combined control group Control group A Control group B 1 2 3 4 5 6 Months Figure 1. Retention in a treatment programs for cocaine dependence. CRA community reinforcement approach. The mean number of weeks patients were retained during the 24 weeks of treatment was 19.2 7.6 in the CRA plus high-vouchers condition, 17.1 8.4 in CRA plus low vouchers, and 14.4 8.5 in standard treatment. There were no statistical difference between control Group A (M 15.4, SD 8.3) and control Group B (M 13.9, SD 8.6), t(50) 0.61, p.54. We found statistical differences at p.05 for the three conditions, F(2, 93) 3.31, p.04. The effect size calculated using eta squared was.07 (medium size). Post hoc comparison indicated that only the mean for the high-vouchers group was significantly different from that of standard treatment. The low-vouchers group did not differ significantly from any other condition. Discussion The main objective of the present study was to determine the effects of reinforcer magnitude (voucher value) on retention and cocaine abstinence in an outpatient treatment for cocaine addiction. In parallel with this aim, a second objective was to determine the effectiveness of a CM intervention in a European cultural context, in a community setting, and in a combined individual group format. Effects of Reinforcer Magnitude With regard to the first objective, each of the treatments assessed in this study was associated with improvements in cocaine abstinence. Nevertheless, both vouchers groups obtained higher rates of abstinence than standard treatment. As regards continuous abstinence, our data are similar to those of previous studies. In such studies, mean continuous abstinence is around 10 weeks, and percentage of participants maintaining abstinence for 6 months of treatment is around 25% (Higgins et al., 1994, 2007). In our case, the mean duration was 15 weeks, and percentage of participants remaining abstinent for the full 6 months was 35.6% (mean for the two vouchers groups). Treatment retention was better in the CRA plus highvouchers group than in the standard treatment group. In fact, the percentage of patients who completed 24 weeks of treatment in the CRA plus high-vouchers condition was almost double the figure for the standard treatment condition (69% vs. 36.5%). Retention was also better in the highthan low-vouchers condition, and in this latter group than in the standard group. Nevertheless, these differences did not attain statistical significance. Retention rate in the high-vouchers condition after 6 months of treatment is similar to those obtained in previous studies (Dallery et al., 2001; Higgins et al., 1994, 2003, 2007; Higgins, Wong, Badger, Ogden, & Dantona, 2000). In those works, retention rates ranged from 56% to 75%, the latter figure being obtained in one of the earliest studies, with a sample of 40 patients (Higgins et al., 1994). All subsequent work obtained retention rates slightly lower than those of the 1994 research and, in turn, lower than those obtained in the present study. It should be mentioned, however, that in many previous studies, the intensity of reinforcement from the 3rd to the 6th month was reduced more than it was here. In our case, we moved from a continuous reinforcement program, in the first 12 weeks, to one of intermittent reinforcement, with a probability of 50%. In the previous studies to which we refer, the reinforcers during this period consisted of a lottery ticket worth $1 for each negative analysis. The suggestion is, therefore, that maintaining the same type of reinforcer (vouchers exchangeable for different goods and services) and the same reinforcement program (although intermittent rather than continuous) during the latter 3 months may improve treatment retention rates. The relationship between reinforcer magnitude and retention does not follow a constant function; rather, its effect is greater with the passage of time. Whereas in the CRA plus low-vouchers group the retention rates during the first 2 months are practically the same as those in the CRA plus high-vouchers group, after the 3rd month the retention rate

VOUCHER-BASED INTERVENTION FOR COCAINE ADDICTION 137 falls more quickly in the low-vouchers group than in the high-vouchers group, although differences between the two groups were not statistically significant. We should stress the difficulty of comparing the results of our study with those obtained in previous studies with North American samples. Not only are the programs applied in different contexts, but also the participants are, at least to some extent, different especially as regards the administration route for the drug, which is preferentially smoked in the United States, whereas in Spain intranasal administration is more common. This means that the addiction severity of our patients may be lower than that of patients from other studies, so that the outcomes are not fully comparable. The abstinence and retention rates for the treatments implemented are of unquestionable clinical relevance because the results of multiple studies show how retention and abstinence during the first weeks of treatment are the most important predictors of long-term abstinence (Bovasso & Cacciola, 2003; Carroll, Power, Bryant, & Rounsaville, 1993; Higgins, Badger, & Budney, 2000; Higgins et al., 2007). The current study set out to build on previous clinical and experimental research suggesting that reinforcer magnitude is a determinant variable for treatment outcomes (Dallery et al., 2001; Higgins et al., 2007). In our view, the fact that the differences between the two vouchers groups failed to attain statistical significance could be due to the small sample size. Furthermore, there is little drug use detected among patients and therefore most of the urinalysis results were negative. This ceiling effect among patients can be a limitation for detecting differences between groups. Nevertheless, the data indicate a clear tendency for better results in the highvouchers group compared with the low-vouchers group. Contingency Management Beyond the United States The majority of studies on CM interventions have been carried out in the United States. The value of the present study is that the CM intervention was conducted in a novel setting (Spain), demonstrating its effectiveness outside the United States. The results in dependent variables (cocaine abstinence and retention), compared with a standard treatment, support the general efficacy of the approach, and the effects of reinforcer magnitude were wholly consistent with those of previous studies on CM programs. Moreover, the present study indeed supports the generalizability of a specific CM and psychological program for cocaine addiction, the CRA plus vouchers approach, beyond the United States and with similar levels of efficacy. One of the major barriers to the transfer of CM interventions to community settings is the high cost. For this reason, an important current focus in this area of research is the development of less costly models. The literature shows that cost can be reduced by lowering the reinforcer magnitude without totally losing efficacy, but that effect size is reduced as magnitude is decreased (Petry, Alessi, Marx, Austin, & Tardif, 2005). Thus, there is a need to seek ways of reducing costs other than by lowering magnitude. Drug dependence treatments are usually implemented in a group-based format, so that in the present study we applied most of the CRA components (drug avoidance skills, lifestyle change components, and other substance abuse) in this customary way of treating addicts in community settings. This could be an alternative form of reducing the costs derived from the CRA program. As reported elsewhere, the CRA approach involves different psychological strategies that can be perfectly adapted to a group intervention (Secades-Villa et al., 2008). Cocaine abstinence and retention rates were quite similar to those reported in previous studies using individual therapy sessions (Higgins et al., 1994, 1993). Nevertheless, these results would need to be confirmed with a different design, comparing CRA delivered in group-based versus individual-based sessions. The main limitation of the present study is the betweenclinics design because effectiveness between clinics could have been as great as effectiveness between groups. Nevertheless, as outcomes were equivalent across the two control groups, the conclusions of this trial can be considered as valid. The results suggest that the CRA plus vouchers program model is applicable outside the United States, and that it can be adapted to the natural conditions imposed by a real community care context in Spain. References American Psychiatric Association. (2000). Diagnostic and statistical manual of mental disorders (4th ed., text rev.). Washington, DC: Author. Beck, A. T., Ward, C. H., Mendelson, M., Mock, J., & Erbaugh, J. (1961). An inventory for measuring depression. Archives of General Psychiatry, 4, 561 571. Bickel, W. K., Marsch, L. A., Buchhalter, A. R., & Badger, G. J. (2008). Computerized behavior therapy for opioid-dependent outpatients: A randomized controlled trial. Experimental and Clinical Psychopharmacology, 16, 132 143. Bovasso, G., & Cacciola, J. (2003). The long-term outcomes of drug use by methadone maintenance patients. Journal of Behavioral Health Services & Research, 30, 290 303. Budney, A. J., & Higgins, S. T. (1998). A community reinforcement plus vouchers approach: Treating cocaine addiction. Rockville, MD: National Institute on Drug Abuse. Carroll, K. M., Power, M. E., Bryant, K., & Rounsaville, B. J. (1993). One-year follow-up status of treatment-seeking cocaine abusers. Psychopathology and dependence severity as predictors of outcome. Journal of Nervous and Mental Disease, 181, 71 79. Cohen, J. (1988). Statistical power analysis for the behavioral sciences. Hillsdale, NJ: Erlbaum. Dallery, J., Silverman, K., Chutuape, M. A., Bigelow, G. E., & Stitzer, M. L. (2001). Voucher-based reinforcement of opiate plus cocaine abstinence in treatment-resistant methadone patients: Effects of reinforcer magnitude. Experimental and Clinical Psychopharmacology, 9, 317 325. European Monitoring Centre for Drugs and Drug Addiction. (2007). Annual report 2007. Luxembourg: Office for Official Publications of the European Communities. Garcia-Rodriguez, O., Secades-Villa, R., Alvarez Rodriguez, H., Rio Rodriguez, A., Fernandez-Hermida, J. R., Carballo, J. L., et al. (2007). Efecto de los incentivos sobre la retención en un tratamiento ambulatorio para adictos a la cocaína [Effect of incentives on retention in an outpatient treatment for cocaine addicts]. Psicothema, 19, 134 139. Garcia-Rodriguez, O., Secades-Villa, R., Higgins, S. T., Fernandez- Hermida, J. R., & Carballo, J. L. (2008). Financing a voucher

138 GARCIA-RODRIGUEZ ET AL. program for cocaine abusers through community donations in Spain. Journal of Applied Behavior Analysis, 41, 623 628. Higgins, S. T., Badger, G. J., & Budney, A. J. (2000). Initial abstinence and success in achieving longer term cocaine abstinence. Experimental and Clinical Psychopharmacology, 8, 377 386. Higgins, S. T., Budney, A. J., Bickel, W. K., Foerg, F. E., Donham, R., & Badger, G. J. (1994). Incentives improve outcome in outpatient behavioral treatment of cocaine dependence. Archives of General Psychiatry, 51, 568 576. Higgins, S. T., Budney, A. J., Bickel, W. K., Hughes, J. R., Foerg, F., & Badger, G. (1993). Achieving cocaine abstinence with a behavioral approach. American Journal of Psychiatry, 150, 763 769. Higgins, S. T., Delaney, D. D., Budney, A. J., Bickel, W. K., Hughes, J. R., Foerg, F., et al. (1991). A behavioral approach to achieving initial cocaine abstinence. American Journal of Psychiatry, 148, 1218 1224. Higgins, S. T., Heil, S. H., Dantona, R., Donham, R., Matthews, M., & Badger, G. J. (2007). Effects of varying the monetary value of voucher-based incentives on abstinence achieved during and following treatment among cocaine-dependent outpatients. Addiction, 102, 271 281. Higgins, S. T., Sigmon, S. C., Wong, C. J., Heil, S. H., Badger, G. J., Donham, R., et al. (2003). Community reinforcement therapy for cocaine-dependent outpatients. Archives of General Psychiatry, 60, 1043 1052. Higgins, S. T., Wong, C. J., Badger, G. J., Ogden, D. E., & Dantona, R. L. (2000). Contingent reinforcement increases cocaine abstinence during outpatient treatment and 1 year of follow-up. Journal of Consulting and Clinical Psychology, 68, 64 72. Kokkevi, A., & Hartgers, C. (1995). European adaptation of a multidimensional assessment instrument for drug and alcohol dependence. European Addiction Research, 1, 208 210. Lussier, J. P., Heil, S. H., Mongeon, J. A., Badger, G. J., & Higgins, S. T. (2006). A meta-analysis of voucher-based reinforcement therapy for substance use disorders. Addiction, 101, 192 203. Petry, N. M., Alessi, S. M., Marx, J., Austin, M., & Tardif, M. (2005). Vouchers versus prizes: Contingency management treatment of substance abusers in community settings. Journal of Consulting and Clinical Psychology, 73, 1005 1014. Prendergast, M., Podus, D., Finney, J., Greenwell, L., & Roll, J. (2006). Contingency management for treatment of substance use disorders: A meta-analysis. Addiction, 101, 1546 1560. Secades-Villa, R., Garcia-Rodriguez, O., Higgins, S. T., Fernandez- Hermida, J. R., & Carballo, J. L. (2008). Community reinforcement approach plus vouchers for cocaine dependence in a community setting in Spain: Six-month outcomes. Journal of Substance Abuse Treatment, 34, 202 207. Selzer, M. L. (1971). The Michigan Alcoholism Screening Test: The quest for a new diagnostic instrument. American Journal of Psychiatry, 127, 1653 1658. Sindelar, J., Elbel, B., & Petry, N. M. (2007). What do we get for our money? Cost-effectiveness of adding contingency management. Addiction, 102, 309 316. United Nations Office for Drugs and Crime. (2007). World drug report 2007. Vienna, Austria: United Nations. Received September 9, 2008 Revision received March 19, 2009 Accepted March 27, 2009