Our findings indicate that older African Americans and Caucasians (both Hispanic and non-Hispanic) had a greater odds of study retention than younger African Americans when considering only client characteristics. Primary drug of abuse was also a significant factor in determining study retention. In considering factors related to the nature of study protocols, after adjustment for our client level factors, we were unable to develop a multivariable model due to high correlation among protocol variables. When we performed univariate analyses separately testing treatment program characteristics, we found that only the presence of HIV risk screening, decreasing levels of female admissions (as a percent of total admissions), were related to study retention. The age by race/ethnicity interaction term with a p-value of 0.11 was not significant by the criterion we chose (0.10). There appears to be some confounding with HIV risk screening, as without HIV risk screening, the interaction term was significant by our criterion in the client and protocol models.
Clearly, retention of study participants in drug treatment trials is a complex phenomenon. Person-level characteristics, age and substance of abuse, were enduring and remained significant even in the presence of protocol and program level variables. The finding associating retention with primary drug of abuse is not surprising. Previous studies have found high treatment attrition rates for individuals with polydrug and stimulant use disorders [14
]. Individuals with heroin and opiate use disorders are often either receiving opiate replacement or detoxification services; thus, leaving treatment prematurely would result in adverse physical symptoms. Although these findings from the literature relate to treatment retention, they parallel our findings for study retention. Thus, studies 1 and 2, which were designed for opioid dependent subjects and had a short intervention (13 days), would be expected to have high study retention rates.
Unfortunately, in our analysis of protocol factors, we only had six different protocols to consider, and for protocols 1 and 2 as well as for protocols 6 and 7 the only differences were in setting - not procedures. Thus, our ability to study the impact of protocol variability was reduced. Nevertheless, the lack of a detectable association between either maximum potential compensation for study participation and its surrogate, length of study intervention and retention is intriguing.
More difficult to interpret are our program level findings. We were surprised that offering HIV risk screening was important. This service may be an indicator of more comprehensive services in general, or it may represent a need that is being filled for clients, and thus a programmatic approach that encourages retention. It is also possible that the presence of HIV risk screening is indicative of other ancillary services that encourage `one stop shopping,' thus providing multiple reasons for returning to the treatment center - again with a positive impact for study retention.
At the program level, we were also surprised to find that the programs with high annual percent of female admissions have relatively low retention rates. While gender itself (at the client level) was not a significantly related to retention, at the program level decreasing percentages of female admissions were related to higher retention. We have no clear explanation for this finding.
A number of publications outline challenges in retention of minority participants in research projects, as well as strategies for improved retention (e.g., [17
]). In a qualitative study of HIV positive drug users who were participants in a nutritional chemoprevention trial, Moreno-Black et al.
] found that three themes emerged for continuation in the study: increased health awareness, personal enhancement, and sociability. It may be that treatment centers with HIV risk screening actually tapped into and enhanced participant health awareness, thus positively affecting study retention.
The strengths of this analysis are that it includes a large number of drug abuse treatment clients from geographically disperse areas throughout the United States. It also includes multiple studies representing different types of interventions. We had the ability to look at programmatic characteristics that might be influential in study retention. Thus, the ability to look at characteristics from these three levels (client, protocol, and program-matic) represents a major advance.
As limitations, only three therapy types were represented among the six studies, we did not have data on all programmatic variables that could influence retention, and there was limited variability among protocols. For example, number of intervention sessions may be important, but was not used in this study because we had one protocol that was conducted during an inpatient stay making it difficult to quantify this variable for that study. In addition, since protocol length and compensation were directly related, we could not study these variables separately. Importantly, we were not able to measure race/ethnicity or gender of the staff who actually conducted study follow-up assessments, and this may have been a key influence on study retention. We also had to drop from analysis minority groups other than Hispanic and African American and those who were of multi-race/ethnicity due to small numbers. It should also be noted that two protocols (CTN 6 and 7) published on an earlier retention endpoint (12 weeks) than the endpoint specified in the protocol due to poor study retention at the later time point. Since we were interested in retention, we used the protocol specified end point.
Future studies of retention could build off of these findings. Our data suggest, at least for substance abuse studies, that special attention needs to be paid to younger participants with a suggestion of a need for particular focus on young African Americans and that offering onsite HIV testing could be a useful incentive. Future studies including a wider range of minority groups, expanding the protocol types, and assessing additional programmatic features such as race/ethnicity of study interviewers would be useful in developing future retention interventions for all race/ethnicity groups.