Abstract
BackgroundNatural experiments are increasingly valued as a way to assess the health impact of health and non-health interventions when planned controlled experimental research designs may be infeasible or inappropriate to implement. This study sought to investigate the value of natural experiments by exploring how they have been used in practice. The study focused on obesity prevention research as one complex programme area for applying natural experiment studies.MethodsA literature search sought obesity prevention research from January 1997 to December 2017 and identified 46 population health studies that self-described as a natural experiment.ResultsThe majority of studies identified were published in the last 5 years, illustrating a more recent adoption of such opportunities. The majority of studies were evaluations of the impact of policies (n = 19), such as assessing changes to food labelling, food advertising or taxation on diet and obesity outcomes, or were built environment interventions (n = 17), such as the impact of built infrastructure on physical activity or access to healthy food. Research designs included quasi-experimental, pre-experimental and non-experimental methods. Few studies applied rigorous research designs to establish stronger causal inference, such as multiple pre/post measures, time series designs or comparison of change against an unexposed group. In general, researchers employed techniques to enhance the study utility but often were limited in the use of more rigorous study designs by ethical considerations and/or the particular context of the intervention.ConclusionGreater recognition of the utility and versatility of natural experiments in generating evidence for complex health issues like obesity prevention is needed. This review suggests that natural experiments may be underutilised as an approach for providing evidence of the effects of interventions, particularly for evaluating health outcomes of interventions when unexpected opportunities to gather evidence arise.
Highlights
Natural experiments are increasingly valued as a way to assess the health impact of health and nonhealth interventions when planned controlled experimental research designs may be infeasible or inappropriate to implement
Literature search strategy A literature review was conducted on published peerreviewed studies that self-described as natural experiments and focused on obesity prevention through improving nutrition or physical activity
A further 37 studies were removed as a commentary or opinion piece (n = 6), a protocol or methods article (n = 7), a review or metaanalysis (n = 8), or unrelated to obesity prevention (n = 12); an additional 4 four studies were removed as they did not self-identify as natural experiments (Additional file S2)
Summary
Natural experiments are increasingly valued as a way to assess the health impact of health and nonhealth interventions when planned controlled experimental research designs may be infeasible or inappropriate to implement. The study focused on obesity prevention research as one complex programme area for applying natural experiment studies. Many public health issues are complex, requiring preventive health actions targeted at multiple upstream social and environmental determinates to improve population-level outcomes [1]. The published literature is almost entirely focused on short-term individual-level research outcomes and lacking complex, multi-level, population-level intervention evidence [2]. Obesity is recognised as a complex health issue, driven by multiple interrelated factors, including environmental, social and cultural determinants beyond individual-level determinants of behaviour [3–5]. Effective population-wide prevention strategies implemented at-scale are needed to combat obesity; individually targeted strategies, such as health education and behavioural skills, have largely been found to be ineffective and unsustainable [2, 7]. The effectiveness of these interventions or policies remains limited by a lack of evaluation evidence
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