to obesity prevention have been highlighted in previous Institute of Medicine (IOM) reports (IOM, 2005, 2007).

To obtain an overview of the status of the existing relevant evidence base, the committee examined studies published over the past 13 years to identify reviews focused on obesity prevention. This examination was not meant to be exhaustive, but to illustrate the scope of existing appraisals and the criteria used to determine what studies did or did not qualify for inclusion. Nearly 50 such reviews, hereafter referred to as “appraisals,” were identified (see Appendix C). Approximately half of these appraisals consider literature published as early as 1980, and several include literature from as early as 1966 and/or the inception of the search databases used. The appraisals consist of meta-analyses, systematic reviews, integrative reviews, a review of reviews, evidence syntheses, best practice summaries, and task force recommendations. Nearly one-third of the appraisals were published in journals specific to obesity; the other two-thirds appeared in journals focused on medicine, preventive medicine, public health, health promotion, family and community health, health education, nutrition, nursing, epidemiology, endocrinology and metabolism, and psychology. Almost three-quarters of the appraisals had been published since 2005, indicating the increased interest in the topic. This examination of the literature revealed the challenges involved in applying traditional evidence hierarchies to population-based prevention efforts, as described below.

Quantity of Available Evidence

In the appraisals examined, the number of studies found eligible for inclusion ranges from 3 to 158, a small percentage of the number of studies initially identified for potential further analysis, which ranged from 12 to 13,158. However, while all of the appraisals report the number of studies found eligible for inclusion, some do not report the number of studies initially identified. The range of studies included reveals a clear discrepancy between what authors of specific studies might think of as obesity prevention research and what authors of reviews consider to be part of the evidence base. There is considerable overlap in studies included in these appraisals; however, conclusions vary as to what is effective. Furthermore, most studies included in the appraisals lack detail about the process of the interventions and process evaluation information. Several of the appraisals explicitly address what types of evidence should be considered relevant, whether one fails to be comprehensive by restricting evidence to randomized controlled trials (RCTs) with rigorous inclusion and exclusion criteria, and whether literature searches should extend beyond well-known databases and include monographs or reports not published in peer-reviewed journals.

Lack of Conceptual Frameworks

The lack of a conceptual framework specifically related to evidence selection has resulted in the majority of appraisals failing to draw conclusions about the most effec-

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