Use of GRADE in systematic reviews of health effects on pollutants and extreme temperatures: A cross-sectional survey.

Objectives: (i) To analyze trends and gaps in evidence of health effects on pollutants and extreme temperatures by evidence mapping; (ii) to conduct a cross-sectional survey on the use of the Grades of Recommendations Assessment Development and Evaluation (GRADE) in systematic reviews or meta-analyses (SR/MAs) of health effects on pollutants and extreme temperatures.

Study Design And Setting: PubMed, Embase, the Cochrane Library, Web of Science, and Cumulative Index to Nursing and Allied Health Literature (CINAHL) were searched until July 7, 2022. SR/MAs investigated health effects of pollutants and extreme temperatures were included.

Results: Out of 22,658 studies, 312 SR/MAs were included in evidence mapping, and the effects of pollutants on cancer and congenital malformations were new research hotspots. Among 16 SR/MAs involving 108 outcomes that were rated using GRADE, the certainty of evidence was mostly downgraded for inconsistency (50, 42.7%), imprecision (33, 28.2%), and risk of bias (24, 20.5%). In contrast, concentration-response gradient (26, 65.0%) was the main upgrade factor.

Conclusion: GRADE is not widely used in SR/MAs of health effects on pollutants and extreme temperatures. The certainty of evidence is generally low, mainly because of the serious inconsistency or imprecision. Use of the GRADE in SR/MAs of health effects on pollutants and extreme temperatures should strengthen.