Table 4.

Assessment of risk of bias for included NRS

Author	Selection	Comparability	Outcome
Boersma et al. [77]a	★ ★ ★ ★		★ ★ ★
Tay et al. [78]b	★ ★ ★ ★	★ ★	★ ★ ★
Verbeek et al. [79]a	★ ★ ★ ★	★ ★	★ ★
Villar et al. [80]a	★ ★ ★ ★		★

^aProspective, longitudinal quasi-experimental trials, assessed as cohort by proxy, ^bProspective naturalistic cohort study. Note: A study can be awarded a maximum of one star for each numbered item within the Selection (4 stars) and Outcome (3 stars) categories. A maximum of two stars can be given for Comparability. Maximum no. of stars in total is nine.