. "5 Specifying Questions and Locating Evidence: An Expanded View." Bridging the Evidence Gap in Obesity Prevention: A Framework to Inform Decision Making. Washington, DC: The National Academies Press, 2010.
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Bridging the Evidence Gap in Obesity Prevention: A Framework to Inform Decision Making
address “Why” and “How” questions. For example, Manning and colleagues (1991) assess the economic costs of poor health behaviors, including a sedentary lifestyle. This information can be helpful in addressing why something should be done to increase the level of physical activity in a community. Using data from the National Health Interview Survey and the RAND Health Insurance Experiment, the authors employ an incidence-based approach to determine the lifetime costs of a sedentary lifestyle. Table 5-7 provides examples of the uses of this type of evidence.
Evidence Synthesis Methods
Evidence synthesis methods encompass systematic reviews, and meta-analyses of experimental and/or quasi-experimental studies, syntheses of qualitative research, and mixed-method evidence syntheses. Evidence synthesis is particularly useful in answering “What” questions, but may also be useful for assembling information to address “Why” and “How” questions. Table 5-8 provides examples of how this type of evidence might be used.
The literature on evidence synthesis distinguishes between primary studies, or individual studies presenting original data, and systematic reviews, or organized summaries of a body of research that addresses a focused question using methods intended to reduce the likelihood of bias. Traditional methods of evidence synthesis (in the evidence-based medicine tradition) have relied heavily on quantitative methods, such as meta-analysis, to generate summaries of research-based evidence (see Hunt, 1997; Smith and Glass, 1977). Several systematic reviews relevant to obesity prevention are listed in Appendix C. Some of the limitations of this type of evidence synthesis when applied to public health issues are discussed in Chapter 3.
TABLE 5-7 Types of Mixed-Method Evidence and Examples of Their Uses
Type of Evidence
Questions That Can Be Addressed
Surveys Combined with Randomized Controlled Trial (RCT)
What self-reported individual-, family-, and community-level factors moderate effects on obesity outcomes when an intervention is randomly assigned to one of two adult groups? (“What” question)
A randomized controlled trial of a manipulated nutrition program using two groups of obese adults, with survey-based data of individual-, family-, and community-level factors analyzedas potential moderators of outcomes
Qualitative Analysis Combined with Quasi-experimental Study
Is there qualitative evidence to show that an intervention was implemented as intended when outcomes improved in a time series analysis? How consistently and authentically was the intervention implemented when effects were obtained? (“What” questions)
A content analysis of food logs, menus, and meal plans combined with an interrupted time seriesstudy tracking changes in obesity outcomes when a nutrition program is implemented periodically