Table 1.

Steps from existing systematic review frameworks and modifications needed (if relevant) to apply the steps to systematic reviews of prevalence studies of environmental and occupational risk factors to human health

Framework step	Modifications needed?
Specify research question	Yes – not usually a comparator, no outcome
Protocol	No – basic general step of systematic review
Systematic search	No – basic general step of systematic review
Defining eligibility criteria and screening studies	No – basic general step of systematic review
Data extraction	Yes – new data extraction categories and items are needed
Risk of bias assessment	Yes – risk of bias tools need to be adapted to prevalence study designs
Synthesis	Yes – meta-analyses need to account for ceilings and floors for prevalence and levels of exposure
Certainty of body of evidence assessment	Yes – certainty assessment frameworks need to be adapted for prevalence evidence