Special Diabetes Program for Indians: Retention in Cardiovascular Risk Reduction

The recruitment of individuals into intervention trials has garnered increasing attention as it has become clear that a number of factors, such as gender, age, race/ethnicity, and disease status, systematically as well as differentially affect individual decisions to participate in these efforts (Blanton et al., 2006; D. M. Brown et al., 2006; Coday et al., 2005). There is mounting evidence that biases of this nature compromise representativeness, estimates of effects or rates, and generalizability of results, thereby undermining the confidence one can place in the preventative or treatment approaches under study (Lachin & Foulkes, 1986; Matts, Launer, Nelson, Miller, & Dain, 1998). In response, March 1994, the National Institutes of Health introduced a specific policy mandating the recruitment of racial/ethnic minorities and women into publicly funded clinical research (http://grants.nih.gov/grants/funding/women_min/guidelines_update.htm; Hohmann & Parron, 1996). Although this attention to recruitment was long overdue, much less consideration has been given to the consequences of the differential retention of participants once engaged in a study or trial. Retention is just as important as recruitment to the conclusions one may draw from intervention trials. Like recruitment, retention also affects statistical power, bias, and generalizability (Robinson, Dennison, Wayman, Pronovost, & Needham, 2007). Low retention rates affect the power to detect differences in outcomes (Lachin & Foulkes, 1986). Differential retention of subgroups—defined, for example, in terms of gender, age, or race/ethnicity—compromises comparison, especially if subgroup membership is related to the outcome of interest (Good & Schuler, 1997). Generalizability of results is diminished to the extent that the characteristics of those who dropped out of an intervention study are different from those who were retained (Curry & Jackson, 2003). A wide range of factors appears to affect whether or not an individual remains in a trial. There is, for example, ample documentation that men are more likely than women to be lost to follow-up (Bailey, Bieniasz, Kmak, Brenner, & Ruffin, 2004; D. R. Brown, Fouad, Basen-Engquist, & Tortolero-Luna, 2000; Hessol et al., 2001; Neill & Chessa, 1998; Shumaker, Dugan, & Bowen, 2000); that older adults—barring functional impairments and issues of access—are likely to participate more fully than younger adults (Anderson, Ory, Cohen, & McBride, 2000; Cassidy, Baird, & Sheikh, 2001; Thornquist, Patrick, & Omenn, 1991); that individuals of higher rather than lower socioeconomic status are more likely to be retained (Warren-Findlow, Prohaska, & Freedman, 2003); that African Americans as well as American Indians are at greater risk of dropout than Whites or Asian Americans (Blumenthal, Sung, Coates, Williams, & Liff, 1995; D. R. Brown & Topcu, 2003; Dilworth-Anderson & Williams, 2004; Gorelick, Harris, Burnett, & Bonecutter, 1998; Noe et al., 2007; Shavers, Lynch, & Burmeister, 2002); that depression, anxiety, and alcohol involvement shorten exposure (Chang, Brown, & Nitzke, 2009; Gappoo et al., 2009; Hessol et al., 2001; Katon et al., 2004; Villcorta et al., 2007; Williams, Powers, Yun, & Foa, 2010); and that being single with multiple children contributes to limited availability and infrequent attendance (Gappoo et al., 2009). With respect to staff/provider characteristics, it has been shown that women generally are more effective than men in retaining participants of both sexes (Tansey, Matte, Needham, & Herridge, 2007); that older staff—to the extent that they are seen as mature, experienced, and respected—are more successful than their younger counterparts in sustaining involvement (Blanton et al., 2006; Blumenthal et al., 1995); that staff training, expertise, and professional education correlate highly with decisions to remain in a trial (Booth, Corsi, & Mikulich-Gilbertson, 2004; D. M. Brown et al., 2006); and that interpersonal skills such as personalized attention, empathy, and support result in higher rates of completion (Cassidy et al., 2001). Various features of the site at which an intervention is mounted also are known to relate to adherence. Well-described examples include settings that are welcoming, non-stigmatizing, able to ensure privacy, easily accessible, and located near relevant resources (Gappoo et al., 2009; Warren-Findlow et al., 2003; Williams et al., 2008). Turning to retention strategies, Robinson and colleagues (2007) meta-analysis of the relevant literature identified 12 basic themes, including community involvement, study identity, reminders, contact and scheduling methods, and financial incentives. No optimal strategy emerged; rather, successful retention was associated with a combination of multiple strategies. Their review found that programs with higher retention rates adopted an average of 21 different strategies cutting across several themes. Yet, in reality, these observations are not as consistent as this brief review may suggest. The truer picture likely reflects a complicated interaction of participant, provider/staff, study/program, and site characteristics as well as retention strategies. For example, the personal salience of the health condition at issue (Noe et al., 2007), and ethnic match of participant and staff (Parra-Medina et al., 2004; Shavers et al., 2002), as well as participants’ previous research or intervention experiences (Marcellus, 2004; Mazzuca et al., 2004) have been strongly associated with the quality and duration of engagement in intervention trials. We sought to advance this line of inquiry by examining the relative contribution of participant, staff/provider, and site characteristics to retention in a nationwide intervention aimed at reducing the risk of cardiovascular disease (CVD) in American Indians and Alaska Natives (AI/ANs) with diabetes. The Special Diabetes Program for Indians Healthy Heart (SDPI-HH) Demonstration Project employed an intensive case-management approach to promote the Indian Health Service's (IHS) existing standards of care, which are generally recognized as state of the art in our country's public health system. SDPI-HH was subjected to a rigorous, multilevel evaluation that chronicled participant outcomes over time and provided the data to address the questions before us.