Table 2.

Risk of bias assessment *.

	Confounding	Selection	Classification of Interventions	Deviations from Interventions	Missing Data	Outcome Measurement	Selection of Reported Results	Overall Risk
Bouvier et al. [21]	●	●	●	●	●	●	●	●
Kopac et al. [22]	●	●	●	●	●	●	●	●
Ballmer-Weber et al. [23]	●	●	●	●	●	●	?	●
Bohle et al. [24]	●	●	●	●	●	●	●	●
Hansen et al. [25]	●	?	●	●	●	●	●	●
Worm et al. [26]	●	●	●	●	●	●	●	●
Asero et al. [27]	●	●	●	●	●	●	●	●
Bolhaar et al. [28]	●	●	●	●	●	?	●	●
Kootstra et al. [29]	●	●	●	●	●	●	●	●
Vlieg-Boerstra et al. [30]	●	●	●	●	●	●	●	●

* The Robins-I tool was used for Risk of Bias assessment [19]; ● = low risk of bias; ● = moderate risk of bias; ● = high risk of bias; ? = unclear risk of bias.