2. Risk of bias criteria for single‐arm observational studies of interventions.

	Internal validity	External validity
Study group	Selection bias (representative: yes/no) if the described study group consisted of more than 90% of eligible individuals	Reporting bias (well defined: yes/no) if the intervention and number of participants was defined
Follow‐up	Attrition bias (adequate: yes/no) if the outcome was assessed for more than 90% of the study group of interest (++) or if the outcome was assessed for 60% to 90% of the study group of interest (+)	Reporting bias (well defined: yes/no) if the length of follow‐up was mentioned
Outcome	Detection bias (blind: yes/no) if the outcome assessors were blinded to the investigated determinant	Reporting bias (well‐defined: yes/no) if the outcome definition was objective and precise
Risk estimation	Confounding (adjustment for other factors: yes/no) if important prognostic factors (i.e. age, gender) or follow‐up were taken adequately into account	Analyses (well‐defined: yes/no) If the method of analysis was described and the effect of the intervention was quantified