Table 4.

Summary of risk of bias assessment according to the risk of bias (ROB) tool from the National Toxicology Program (NTP)’s Office of Health Assessment and Translation (OHAT) handbook [27,28].

	Ng et al. [29]	Kho et al. [30]	Sweetman et al. [16]	Chung and Wong et al. [31]	Simon et al. [32]	Kam et al. [33]	Millichap and Wainwright [17]	Cha et al. [34]	Hautala et al. [35]	Huguet et al. [36]	Tebeila et al. [37]
Selection bias
Did selection of study participants result in appropriate comparison groups?	PL	PL	PH	PL	DL	DL	PL	PL	DL	DL	PL
Confounding bias
Did the study design or analysis account for important and modifying variables	PH	PH	PH	PH	PL	PL	PH	PH	DL	DL	PL
Exclusion bias
Were outcome data complete without attrition or exclusion from analysis?	PH	PH	PH	PH	PL	PL	PL	PL	PL	PL	PL
Detection bias
Can we be confident in the exposure characterization?	DL	DL	DL	DL	DL	DL	DL	DL	DL	DL	DL
Can we be confident in the outcome assessment?	PL	PL	PL	PL	DL	PL	PL	PL	DL	DL	DL
Selective reporting bias
Were all measured outcomes reported?	DH	DH	DH	DH	PL	DH	DH	PL	DL	DL	DL
Other sources of bias
Were there no other potential threats to internal validity (e.g., statistical methods were appropriate, and researchers adhered to the study protocol)?	DL	DL	DL	DL	DL	DL	DL	DL	DL	DL	DL

Note: PL = probably low; PH = probably high; DL = definitively low; DH = definitively high.