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Position paper

Position paper calls for strengthening of obesity research

Most natural experiments had a high risk of bias and 63% had weak handling of withdrawals and dropouts

Researchers led by a team from Johns Hopkins University School of Medicine have published a position paper recommending changes to improve the evidence for natural experiments in obesity following a systematic literature review. The position paper, ‘Methods for Evaluating Natural Experiments in Obesity: A Systematic Review’, was published in the Annals of Internal Medicine.

Researchers led by Dr Wendy L Bennett from the Johns Hopkins University School of Medicine in Baltimore, believe that rigorous methodological approaches -  including natural experiments - are needed to combat the obesity pandemic. As a result, they sought to identify studies that report effects of programmes, policies, or built environment changes on obesity prevention and control by using measures of obesity or obesity-related health behaviours.

They identified 294 studies (188 US, 106 non-US) were identified, including 156 natural experiments (53%), 118 experimental studies (40%) and 20 (7%) with unclear study design. Studies used 106 (71 US, 35 non-US) data systems; 37% of the US data systems were linked to another data source. For outcomes, 112 studies reported childhood weight and 32 adult weight; 152 had physical activity and 148 had dietary measures. For analysis, natural experiments most commonly used cross-sectional comparisons of exposed and unexposed groups (n = 55 [35%]). Most natural experiments had a high risk of bias and 63% had weak handling of withdrawals and dropouts.

“Many methodologically diverse natural experiments and experimental studies were identified that reported effects of US and non-US programmes, policies, or built environment changes on obesity prevention and control,” they conclude. “The findings reinforce the need for methodological and analytic advances that would strengthen evaluations of obesity prevention and control initiatives.”

In an accompanying position paper, ‘National Institutes of Health Pathways to Prevention Workshop: Methods for Evaluating Natural Experiments in Obesity’, Dr Karen M Emmons from the Harvard TH Chan School of Public Health in Boston, and colleagues identified research gaps and developed recommendations on four issues based on the findings from the systematic review.

The recommendations include maximising use and sharing of existing surveillance and research databases and ensuring efforts to integrate and link databases. They also state that standardised and validated measures of obesity-related outcomes and exposure should be employed for measurement. In terms of study design, guidance, documentation, and communication about methods used should be improved. Cross-cutting recommendations are provided for improving the rigor of natural experiments in obesity.

"To combat the significant public health threat posed by obesity, researchers should continue to take advantage of natural experiments," Emmons and colleagues write. "The recommendations in this report aim to strengthen evidence from such studies."

The study was primarily funded by the National Institutes of Health, Office of Disease Prevention, and Agency for Healthcare Research and Quality (PROSPERO).

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