Table 3.

Quality assessment of included studies according to the quality in prognosis studies (QUIPS) tool

	Median quality score (range)	Maximum score
Study participation	9.5 (2–10)	10
Population described for key characteristics	2	2
Sampling and recruitment described	2	2
Inclusion/exclusion criteria described	2	2
Adequate participation	2	2
Baseline study sample described	2	2
Prognostic factor measurement	8 (5–10)	12
Prognostic factors are clearly described or defined	1.5	2
Continuous variables reported, or appropriate cut-off points used	1.5	2
Prognostic factors are valid and reliable	2	2
Study sample has complete data for prognostic factors	2	2
Same method and setting of measurement for all study participants	2	2
Appropriate methods used for missing prognostic data	0	2
Outcome measurement	6 (5,6)	6
Definition of the outcome described	2	2
Outcome measure and method are valid and reliable	2	2
Same method and setting of measurement for all study participants	2	2
Confounding factor measurement	8 (1–12)	14
Important confounders are measured	1	2
Clear definitions of confounders described	2	2
Measurement of all confounders is valid and reliable	1	2
Same method and setting of measurement for all study participants	1.5	2
Appropriate methods used for missing confounder data	0	2
Important confounders accounted for in the study design	1.5	2
Important confounders accounted for in the analysis	1	2
Analysis	6 (3–8)	8
Sufficient presentation of data to assess the adequacy of the analysis	1.5	2
Strategy for model building appropriate and based on a conceptual model	1.5	2
Adequate selection of model for the design of the study	2	2
No selective reporting of results	2	2
Median quality score of studies	38 (16–45)	50