Table 3.

Study Bias of Included Studies

Author	Year of Publication	Biasa
		Confounding	Selection	Classification of Intervention	Deviation from Intervention	Missing Data	Measurement of Outcomes	Selection of Reported Result
Joly20	2003	High	High	Low	Low	Low	High	Low
Smith30	2003	High	High	Low	Moderate	Low	High	Moderate
Murtagh21	2007	High	High	Low	Low	Low	High	Low
Carson29	2009	High	High	Low	Moderate	Low	Moderate	Low
Ellam	2009	High	High	Low	Low	Low	High	Low
Wong23	2009	High	High	Low	Low	NR	High	Low
Chandna24	2011	High	High	Low	Low	Low	High	Low
Da Silva-Gane11	2012	High	High	Low	Low	Low	High	Low
Hussain33	2013	High	High	Low	Moderate	Low	Moderate	Low
Seow26	2013	High	High	Low	Low	Low	High	Low
Shum25	2013	High	High	Low	Low	Low	High	Low
Brown35	2015	High	High	Low	Low	Low	Moderate	Low
Verberne31	2016	High	High	Low	Low	Low	Moderate	Low
Kwok27	2016	High	High	Low	Moderate	Low	High	Low
Echevers22	2016	High	High	Moderate	Low	NR	High	Low
Verberne31	2016	High	High	Low	Low	Low	Moderate	Low
Reindl-Schwaighofer42	2017	High	High	Moderate	Low	NR	High	Low
Raman32	2018	Moderate	High	Low	Low	Moderate	High	Low
Tam-Tham34	2018	High	High	Moderate	Low	Low	Moderate	Low

Note: Definitions of Domains of Bias according to ROBINS-I⁴⁴

Confounding of intervention effects occurs when one or more prognostic factors (factors that predict the outcome of interest) also predict whether an individual receives one or the other intervention of interest.

Selection: When exclusion of some eligible participants, or the initial follow-up time of some participants, or some outcome events, is related to both intervention and outcome, there will be an association between interventions and outcome even if the effects of the interventions are identical.

Classification of intervention: Bias introduced by either differential or non-differential misclassification of intervention status.

Deviation from intervention: Bias that arises when there are systematic differences between experimental intervention and comparator groups in the care provided, which represent a deviation from the intended intervention(s).

Missing data: Bias that arises when later follow-up is missing for individuals initially included and followed (eg. differential loss to follow-up that is affected by prognostic factors); bias due to exclusion of individuals with missing information about intervention status or other variables such as confounders.

Measurement of outcomes: Bias introduced by either differential or non-differential errors in measurement of outcome data. Such bias can arise when outcome assessors are aware of intervention status, if different methods are used to assess outcomes in different intervention groups, or if measurement errors are related to intervention status or effects.

Selection of reported result: Selective reporting of results in a way that depends on the findings.

^aROBINS-I Tool Risk of Bias Assessment (2016)