Figure 2.

Mask wearing to prevent primary infection, by study design, review of community use of face masks and similar barriers to prevent respiratory illness, 1 January 1980–19 June 2020

CI: confidence interval; df: degrees of freedom; intvn: intervention; M-H: Mantel–Haenszel; RCT: randomised controlled trial.

See Table 1 for study reference numbers, study setting, study design, outcome, comparison (when not allocated arms in RCTs) and any concurrent other intervention in both study arms.