hold promise for the greater relevance and usefulness of the published scientific literature for other decision makers, responding to some of their major concerns.

Specifically in childhood obesity prevention, Klesges and colleagues (2008) examined studies published between 1980 and 2004 that were controlled, long-term research trials with a behavioral target of either physical activity or healthful eating or both, together with at least one anthropometric outcome. Using review criteria for a study’s generalizability to other individuals, settings, contexts, and time frames (external validity) developed by Green and Glasgow (2006), they found that all of the 19 publications that met their selection criteria lacked full reporting on the 24 dimensions of external validity expected in an optimal paper to enable users to judge potential generalizability (see Box 8-3). Median reporting over all elements was 34.5 percent; the mode was 0 percent with a range of 0 percent to 100 percent. Only four dimensions (descriptions of the target audience and target setting, inclusion–exclusion criteria, and attrition rate) were reported in at least 90 percent of the studies. Most infrequent were reports of setting-level selection criteria and representativeness, characteristics of intervention staff, implementation of intervention content, costs, and program sustainability. These limitations of individual studies are also seen and sometimes multiplied in systematic reviews, such as meta-analyses, of whole bodies of literature. The cumulative problems of inadequate reporting of sampling, settings, and interventions have been noted, for example, in meta-analyses of the patient education literature on preventive health interventions in clinical settings (Simons-Morton et al., 1992; Tabak et al., 1991).

These findings provide strong support for the conclusion of Klesges and colleagues (2008) that the aspects of generalizability that potential users need most to see reported more thoroughly in the published evidence are the “3 Rs”: the representativeness of participants, settings, and intervention staff; the robustness of the intervention across varied populations and staffing or delivery approaches; and the replicability of study results in other places. The specific questions most decision makers will have within these broad categories relate to cost (affordability); scalability; and acceptability in particular populations, times, and settings.

Even with more complete reporting on these issues of a study’s generalizability to other populations, gaps will inevitably remain. RCTs can never fill all of the cells in a matrix of potentially relevant evidence representing all combinations of a study’s dimensions of generalizability: population × setting × intervention × time × staffing × other resources. The empty cells in such a matrix require potential users of evidence to make inferential leaps or more studied extrapolations from the existing coverage of the evidence to their own population, setting, intervention, time, staffing, and other resources. In short, users should bring to bear on their decisions their own theories or assumptions about the fit of the evidence to their situation, which will vary along each of the above dimensions.

A particular challenge for obesity prevention, as in some other areas of chronic disease control, is the multiplicity and complexity of these dimensions. For each



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