concerning the level of certainty and generalizability are discussed in greater detail in Chapter 8.
Scientists have always used criteria or guidelines to organize their thinking about the nature of evidence. Much of what we think we know about the causes of obesity and the current obesity epidemic, for example, is based on the evaluation of evidence using existing criteria. In thinking about the development of a contemporary framework to guide decision making in the complex settings of public health, however, the committee decided to advance a broader view of appropriate evaluation criteria. As described in 2005 in a seminal report from the Institute of Medicine (IOM), these decisions need to be made with the “best available evidence” and cannot wait for the “best possible evidence” or all the desirable evidence to be at hand (IOM, 2005, p. 3). The L.E.A.D. framework should serve the needs of decision makers focused on the obesity epidemic, but can also provide guidance for those making decisions about complex, multifactorial public health challenges more generally.
The starting point for explaining the committee’s approach to evaluating the quality of evidence for obesity prevention is the seven categories of study designs and different sources of evidence presented in Chapter 5. In Table 6-1, this typology is linked to criteria for judging the quality of evidence, drawing on the concept of “critical appraisal criteria” of Rychetnik and colleagues (Rychetnik et al., 2002, 2004). Generally speaking, different types of evidence from different types of study designs are evaluated by different criteria, all of which can be found in the literature on evaluating the quality of each type of evidence. In all cases, high-quality evidence avoids bias, confounding, measurement error, and other threats to validity whenever possible; however, other aspects of quality come into play within the broader scope of evidence advanced by the L.E.A.D. framework.
Users of the L.E.A.D. framework can refer to any of the various criteria for high-quality evidence depending on the source of evidence they have located, following the guidance provided in Chapter 5 as well as the references cited in Table 6-1. This process requires some time and effort by an individual or multidisciplinary group with some expertise in evaluating evidence. Despite the availability of the criteria listed in Table 6-1, making judgments about the quality of evidence can still be challenging. One recommended approach is the eight-step process advanced by Liddle and colleagues (1996):
“Select reviewers(s) and agree on details of the review procedure.
Specify the objective of the review of evidence.
Identify strategies to locate the full range of evidence including unpublished results and work in progress.
Classify the literature according to general purpose and study type.