sufficient numbers of the target population (Chinman, Hannah, et al., 2005; Miller and Shinn, 2005). Brown and Liao (1999) note that “even well-designed, efficacious interventions may fail when they are not delivered or implemented at full strength.” These authors opine that an intervention may not succeed if a high level of participation cannot be sustained throughout the intervention period. They note, as well, that an intervention’s benefit vanishes if there is low participation or if the intervention is not delivered to those who are likely to benefit from it. Individual choice to participate is not a major factor in the adoption of universal classroom or school prevention programs by a school because they generally involve all students. The same is not true of programs that require individuals to choose to participate, including most selective or indicated prevention programs. Often, when one of these prevention programs administered individually or by a small group is available in a community, proportionally few families opt to participate in it (Flay, Biglan, et al., 2005).

When there is low individual-level participation, the overall benefit of the program in the community will typically also be low (population-level benefit is the proportion who participate times the effect size for the participants) (Braver and Smith, 1996; Brown and Liao, 1999). The overall effectiveness of family-based prevention programs (Reid, Webster-Stratton, and Hammond, 2003; Spoth and Redmond, 2000; Epstein, 1991; Eccles and Harold, 1996; Sheldon, 2003; Ialongo, Werthamer, et al., 1999) is particularly affected by low participation levels because families often make individual choices to participate, both initially and over time.

For example, a significant number of families enrolled in home visitation programs drop out over the course of two to three years. Ialongo, Werthamer, and colleagues (1999) had reasonably high population-based participation rates (35 percent of all first grade parents attended six of the seven sessions, 13 percent attended none of the sessions), with families on average receiving half the intervention, and positive long-term results. Family-based programs focusing on stressful events, such as divorce (Wolchik, Sandler, et al., 2002; Forgatch and DeGarmo, 1999) or bereavement (Sandler, Ayers, et al., 2003), as well as community-wide parent training (Brody, Murray, 2006b), also require extensive community engagement and recruitment to get acceptable participation levels. A critical concern for family-based programs is to increase participation, particularly for the subset at high risk that could most benefit (Brown and Liao, 1999). In addition, attention is needed for strategies for increasing participation rates in real-world contexts that may not be able to offer the same incentives possible in the research context.

Lack of cultural relevance may contribute to low participation. However, universal family prevention programs designed specifically for specific minority groups (Brody, Murry, 2006b; Prado, Pantin, et al., 2007) have



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