Table 1

Characteristics of QATs and key study quality domains addressed

QAT domain	EPHPPT	CASP	NOS	Liverpool	GATE	ROB
Applicability	RCT, non-randomised trial, cohort, case-control, cross-sectional	RCT, cohort, case-control, diagnostic tests, economic evaluations, qualitative research, systematic reviews	Cohort, case-control	RCT, non-randomised trial, cohort, case-control, cross-sectional	RCT, non-randomised trial, cohort, case-control, cross-sectional	RCT, non-randomised trial, cohort, case-control, cross-sectional

Classification	Checklist	Checklist	Scale	Scale	Checklist	Checklist

Summary score	Qualitative	No	Quantitative	Quantitative	Qualitative	No

Number of components (questions)	8 (22) (only six components included in summary score)	3 (10–12 depending on study design)	9 (9)	8–9 (8–9 depending on study design)	5 (25)	9 (9)

Methods for selecting study population	Yes	Yes	Yes	Yes	Yes	Partial (only for RCTs)

Methods for measuring exposure and outcome variables	Yes	Partial RCT: outcome only cohort: both case-control: exposure only	Yes	Yes	Partial (outcome only)	Partial (outcome only)

Design-specific sources of bias (excluding confounding)	Partial (only for RCTs, non-randomised trials)	Yes	Yes	Yes	Yes (only for RCTs, non-randomised trials)	Partial (only for RCTs, non-randomised trials)

Methods to control confounding	Yes	Yes	Yes	Yes	Yes	Yes

Statistical methods (excluding control of confounding)	Partial (not included in summary score)	Partial (no decision made about quality)	No	No	Yes	No

Conflict of interest	No	No	No	No	No	No

Major strengths and weaknesses (in addition to features above)	Use is possible without advanced epidemiological training ‘One size fits all’ tool does not do justice to strengths and weaknesses of different study designs	Use is possible without advanced epidemiological training Low inter-rater reliability^* due to combination of main questions and subquestions Too few answer categories for several questions	High inter-rater reliability^* due to very specific answer categories Too few answer categories for several questions	Broad applicability of four companion tools, each geared towards specific study design features Adaptation of considerations on exposure and outcome measurement to systematic review question	Broad applicability of two companion tools, each geared towards specific study design features High inter-rater reliability^* due to very specific questions Combination of indepth assessment of specific limitations with a two-component summary assessment Use requires substantial time investment	Compatibility with the most-widely used tool for systematic reviews of RCTs ‘One size fits all’ tool does not do justice to strengths and weaknesses of different study designs Use requires advanced epidemiological training

↵* Inter-rater reliability was not formally assessed and this statement is based on our subjective experience across the six tools.
CASP, Critical Appraisal Skills Programme; EPHPPT, Effective Public Health Practice Project tool; GATE, Graphical Appraisal Tool for Epidemiological Studies; NOS, Newcastle–Ottawa Scale; QAT, quality appraisal tool; RCT, randomised controlled trial; ROB, Cochrane Collaboration Risk of Bias tool.