Fig 1.
PRISMA 2020 flow diagram for updated systematic reviews, which included searches of databases, registers, and other sources.
Table 1.
Characteristics of the included studies.
Fig 2.
A: Risk of bias summary: review authors’ judgments about each risk of bias item for each included study. B: Risk of bias graph: review authors’ judgments about each risk of bias item presented as percentages across all included studies. The items are scored (+) low risk; (-) high risk; (?) unclear risk of bias.
Fig 3.
Forest plot of the effect of incentive on the response rate.
A: Forest plot of the effect of incentive on the response rate. B: Subgroup analysis for the effect of incentive on the response rate. df: degrees of freedom; I2: I-squared; M-H: Mantel-Haenszel variance; CI: confidence interval.
Fig 4.
Forest plot of the effect of incentive on the consent rate.
A: Forest plot of the effect of incentive on the consent rate. B: A: Subgroup analysis for the effect of incentive on the consent rate. df: degrees of freedom; I2: I-squared; M-H: Mantel-Haenszel variance; CI: confidence interval.