Table 4.

Study quality assessment criteria

Item		Criterion
1	Study design (potential confounders taken into account)	High confidence: RCT, RDD, ITT, instrumental variable
		Medium confidence: DiD with matching, PSM
		Low confidence: other matching
2	Blinding (RCTs only)	High confidence: any blinding or any mention of blinding
		Medium confidence: no blinding
		Low confidence is not used for this item
3	Losses to follow up are presented and acceptable*	High: Overall and differential attrition within WWC combined levels*
		Medium: Overall and differential attrition close to WWC combined levels*
		Low: Attrition not reported, OR falls well outside WWC acceptable combined levels*
4	Disability/impairment measure is clearly defined and reliable	High confidence: Clear definition, for example, Washington Group questions, detailed measure of impairment
		Medium confidence: Unclear definition OR Single question item only (e.g., are you disabled)
		Low confidence: No definition OR overall attrition > 50%
5	Outcome measures are clearly defined and reliable	High confidence: Clear definition using existing measure where possible
		Medium confidence: unclear definition
		Low confidence: no definition
6	Baseline balance (N.A. for before vs. after)	High confidence: RCT, RDD
		Medium confidence: Baseline balance test, imbalance on 5 or fewer measures
		Low confidence: No baseline balance test (except RCT) OR reported and significant differences on more than five measures. PSM without establishing common support.
	Overall confidence in study findings	High: RCT with high confidence on all items
		Medium: Medium or high confidence on all items
		Low: Low on any item