Challenges and recommendations on the conduct of systematic reviews of observational epidemiologic studies in environmental and occupational health

Abstract

Systematic reviews are powerful tools for drawing causal inference for evidence-based decision-making. Published systematic reviews and meta-analyses of environmental and occupational epidemiology studies have increased dramatically in recent years; however, the quality and utility of published reviews are variable. Most methodologies were adapted from clinical epidemiology and have not been adequately modified to evaluate and integrate evidence from observational epidemiology studies assessing environmental and occupational hazards, especially in evaluating the quality of exposure assessments. Although many reviews conduct a systematic and transparent assessment for the potential for bias, they are often deficient in subsequently integrating across a body of evidence. A cohesive review considers the impact of the direction and magnitude of potential biases on the results, systematically evaluates important scientific issues such as study sensitivity and effect modifiers, identifies how different studies complement each other, and assesses other potential sources of heterogeneity. Given these challenges of conducting informative systematic reviews of observational studies, we provide a series of specific recommendations based on practical examples for cohesive evidence integration to reach an overall conclusion on a body of evidence to better support policy making in public health.

Keywords: Alternatives assessment; Environmental health policy; Exposure assessment.

Figure 1:. Elements of a well-conducted systematic review

Developing the systematic framework includes several key components such as a scoping and review of the literature (which identifies key scientific issues to address); development of the framework of the literature to be included in the review (such as the PECO or other types of evidence); the systematic literature search strategy (including inclusion and exclusion criteria); development of methods and protocol (which directs the review process, provides transparency for evaluating study quality and in-depth and cohesive analysis and integration of the evidence across studies. Input from subject matter experts is critical at all steps of a systematic review. Many steps in the systematic review process are iterative and can inform one another. *Not all SR do this at this stage