Table 1

Differences between grading of strength of accuracy and effectiveness evidence

Items	Effectiveness research	Accuracy research	Issues to consider
The basics
Question	Participants, Intervention, Comparator and Outcome(s)	Population, Index test and Reference standard	PICO structure does not readily apply in diagnostic research
Study design	Randomised controlled trial (RCT) Non-randomised controlled studies	Cross-sectional Other designs for index test and reference standard comparison	RCT not required for accuracy evaluations
Measure of performance	Effect estimate (OR or risk ratio)	Accuracy estimates (sensitivity and specificity)	Accuracy estimates are usually paired; global single accuracy measures are not very intuitive
GRADE feature
Risk of bias	Tools for the risk of bias typically assess: random sequence generation, allocation concealment, blinding, incomplete outcome data, selective outcome reporting	Methodological quality part QUADAS-2 instrument includes: participant selection, implementation of the index test, reference standard, flow and timing	Various tools exist; there is no consensus on what is best for accuracy research
Indirectness	Based on PICO question (see above)	QUADAS-2 instrument applicability part can be deployed	Accuracy research requires looking at participants, reference standard, flow and timing
Inconsistency	I² or χ² tests for heterogeneity	Visual assessment of overlap of CIs between studies	Assessed separately for sensitivity and specificity in accuracy research
Imprecision	95% CIs around an effect measure	95% CIs around multiple accuracy measures	Assessed separately for sensitivity and specificity in accuracy research
Publication bias	Test for funnel plot asymmetry	Test for funnel plot asymmetry	Test for funnel asymmetry requires particular caution in accuracy research

PICO, Population Intervention Comparator Outcome; GRADE, Grading of Recommendations Assessment, Development and Evaluation; QUADAS-2, Quality Assessment of Diagnostic Accuracy Studies.