Randomization can be used in highly flexible ways in studies of preventive interventions (Brown, Wyman, et al., 2007; Brown, Wang, et al., 2008), often answering different questions from the traditional randomized trial that focuses on efficacy or effectiveness alone (West, Biesanz, and Pitts, 2000). For example:
Head-to-Head Impact. How beneficial is a preventive intervention program compared with another type of intervention? Preventive interventions can be compared not only with one another, but also with a service-based or treatment approach. In elementary school systems in the United States, for example, many incoming first grade children do not do well in the first couple of years of school; nevertheless, most of these failing children are not provided remedial educational services until the third grade. It is feasible to compare the impact of a universal classroom-based preventive intervention aimed at improving children’s ability to master the social and educational demands at entry into first grade with a more traditional model that provides similar services at a later stage for children in serious need.
Implementability. What effects come from alternative modes of training or delivery of a defined intervention? After demonstrating that an intervention is effective, one can examine different means of implementing that intervention, holding fixed its content. Webster-Stratton (1984, 2000) has used such trials to demonstrate that self-administered videotapes are effective and a cost-effective way of delivering the Incredible Years Program (see Box 6-2) outside the clinic.
Adaptability. How does a planned variation in the content and delivery of a tested intervention affect its impact? For example, the third-generation Home Visitor Trial, conducted by Olds, Robinson, and colleagues (2004) in Denver, compared the delivery of a home-based intervention by a paraprofessional with the standard intervention delivered by nurse home visitors.
Extensibility. What impact is achieved when an intervention is delivered to persons or in settings different from those in the original trial? One question being addressed is whether Olds’s work on nurse home visitors, which originally focused on high-risk new mothers, would work as well for all pregnancies. Encouragement designs (described above) are also extensibility trials, since they can be used to expand the population that would normally participate in these interventions.