Table 1A.

prognostic studies: Quality assessment of the included studies according to the ‘Methodology checklist for prognostic studies.’ All items were scored with a ‘yes’, ‘no’, or ‘unclear’. A ‘yes’ response indicates that the study has been designed and conducted in such a way as to minimize the risk of bias for that item. An ‘unclear’ response was given when the answer to an item is not reported or is not reported clearly.

Study	Population	Drop-out	Prognostic factor	Outcome	Confounders	Statistical analysis	Inclusion?
Iannotti et al22	yes	yes	yes	yes	yes	no	Yes
Toussaint, 201162	yes	no	unclear	yes	unclear	no	Yes
Kim et al11, 23	yes	yes	yes	yes	yes	yes	Yes
Cho and Rhee9	yes	no	yes	yes	unclear	no	Yes
Edwards, 200246	yes	unclear	unclear	unclear	yes	unclear	No
Koh, 201454	yes	no	unclear	yes	unclear	unclear	No
Chung et al10, 19, 38	yes	no	yes	yes	unclear	unclear	Yes
Choi et al18	yes	no	yes	yes	unclear	unclear	Yes
Wiater et al36	yes	unclear	yes	yes	unclear	unclear	Yes
Lapner et al24	yes	unclear	yes	yes	yes	unclear	Yes
Vastamaki, 201363	unclear	unclear	unclear	yes	unclear	no	No
Fuchs et al20	yes	yes	yes	yes	no	yes	Yes
Goutallier, 200349	unclear	unclear	unclear	yes	unclear	no	No
Mellado et al25	yes	unclear	yes	yes	unclear	no	Yes
Goutallier, 200950	yes	unclear	unclear	unclear	unclear	no	No
Zumstein et al37	unclear	yes	yes	yes	unclear	yes	Yes
Nich et al30	yes	unclear	yes	yes	unclear	no	Yes
Park et al39	yes	unclear	yes	yes	yes	yes	Yes
Chung et al10, 19, 38	yes	unclear	unclear	yes	yes	yes	Yes
Kim, 201655	unclear	unclear	unclear	unclear	unclear	unclear	No