Table 4. Cochrane risk-of-bias for assessment of randomized controlled trials (RCTs).

RCT	Selection bias	Reporting bias	Performance bias	Detection bias	Attrition bias
Spanheimer et al. [23]	Low risk	Low risk	Low risk	Intermediate risk	Low risk
Zerp et al. [24]	Low risk	Low risk	Intermediate risk	Low risk	Low risk