Table 2.

QUIPS domain scores for each primary study

Source	Participation	Study attrition	Risk factor measurement	Outcome measurement	Confounding	Statistical analysis and presentation	Overall risk of bias
Case–control studies
Boyle-Walker et al32	High	Moderate	High	Moderate	High	Moderate	High
Li et al33	Moderate	Low	Moderate	High	High	High	High
Lee et al34	Moderate	Low	Moderate	Moderate	High	Moderate	High
Milgrom et al35	Moderate	Low	Low	Low	High	Low	High
Wang et al36	Low	Low	Low	Low	High	Low	High
Kingston et al37	Low	Moderate	Moderate	Low	High	Moderate	High
Cohort studies
Huang et al38	Low	Moderate	Low	High	High	High	High
Lo et al39	Low	Low	Low	Moderate	High	Low	Moderate

QUIPS, Quality In Prognosis Studies.