dence screening and data compilation and analysis can be approached by synthesizing diverse types and sources of evidence.
In a mixed-method synthesis of evidence, Connelly and colleagues (2007) combined a systematic review of eligible quantitative trials with qualitative content analysis of descriptive data on interventions, as reported in the studies. Because the approach relies on the realist philosophy of science that examines causal pathways while acknowledging social realities (as opposed to the logical-positivistic philosophy of traditional laboratory science), this approach to evidence synthesis has been referred to as a “realist review.” The topic was prevention of childhood obesity and overweight. The authors began with a search of four electronic databases (including MEDLINE and PsychInfo) and applied published criteria to screen studies for quality and inclusion (e.g., execution of random assignment or other controls in study designs, sample size, lack of subject attrition, measurement validity and reliability, treatment duration and fidelity). This procedure initially identified 30 RCTs or controlled trials. Trials were included if they had a measured index of adiposity (the outcome), a population aged 0-18, and a 12-week follow-up to treatment. Blind to the study outcomes, the authors then sorted the studies into two categories based on a systematic content analysis of the intervention descriptions provided, using an “intensity of physical activity” indicator. This procedure allowed them to qualitatively separate “compulsory” from “voluntary” activity interventions. The authors then proceeded with the evidence synthesis, summarizing effects found across studies by group. Their conclusions showed that while nutrition education, skills training, and physical education were not effective in controlling childhood obesity, compulsory rather than voluntary physical activity was. Notably, the effects were not evident with the undifferentiated physical activity indicator in the overall sample. According to the authors, their rational, realist review permitted them to link the physical activity type causally with decreases in overweight and obesity.
Parallel practice evidence is an indirect form of research evidence. Evidence of the effectiveness of an intervention in addressing another public health issue using similar strategies—such as the role of social marketing, curriculum programs, or financial factors in reducing smoking, speeding, or sun exposure—may have implications for an obesity-related outcome such as dietary intake. Here, the characteristics of the original research or evaluation reports, such as how the evidence was generated, whether the work was peer-reviewed, where the work is published, and the credentials of the author(s), help determine the quality of the evidence (Swinburn et al., 2005). Should such data be available in the form of a compiled policy brief or legal brief, again the quality of the evidence should be carefully evaluated based on the original data sources. Ideally, information about quality assessment would be incorporated into the report, with an explanation of the criteria used and a clear statement of the study