Table 3.

Quality assessment of non-randomized studies (ROBINS-I Checklist)

	Brenner, 2017	Crilley, 1997	Jansen, 2015	Krasniqi, 2012
Bias due to confounding	Low	Serious	Moderate	Serious
Bias in selection of participants into the study	Low	Low	Moderate	Serious
Bias in classification of interventions	Low	Low	Low	Moderate
Bias due to deviations from intended interventions	Low	Low	Low	Low
Bias due to missing data	Moderate	Serious	Low	Moderate
Bias in measurement of outcomes	Moderate	Moderate	Moderate	Moderate
Bias in selection of the reported result	Low	Low	Low	Low
Overall bias	Low	Moderate	Low	Serious