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Meta-Analysis
. 2022 Apr 22;17(4):e0267534.
doi: 10.1371/journal.pone.0267534. eCollection 2022.

The effectiveness of incentives for research participation: A systematic review and meta-analysis of randomized controlled trials

Basel Abdelazeem  1   2 , Kirellos Said Abbas  3 , Mostafa Atef Amin  4 , Nahla Ahmed El-Shahat  5 , Bilal Malik  1   2 , Atefeh Kalantary  6 , Mostafa Eltobgy  7
Affiliations
Meta-Analysis

The effectiveness of incentives for research participation: A systematic review and meta-analysis of randomized controlled trials

Basel Abdelazeem et al. PLoS One. .

Abstract

Background: Recruitment plays a vital role in conducting randomized control trials (RCTs). Challenges and failure of proper recruitment lead to early termination of trials. Monetary incentives have been suggested as a potential solution to these challenges. Therefore, we aimed to do a systematic review and analysis to evaluate the effect of incentives on the number of participants willing to consent to and participate in RCTs.

Methods: Electronic databases were systematically searched from inception to September 23rd, 2021, using the following keywords: payments, incentive, response, participation, enrollment, randomized, randomization, and RCT. The Cochrane Risk of Bias tool was used to assess the quality of the included trials. Risk ratios (RRs) were calculated with their corresponding 95% confidence interval (CI). All analyses were done with the random-effects model. We used Revman software to perform the analysis.

Results: Six RCTs with 6,253 Participants met the inclusion criteria. Our analysis showed significant improvement in response rate (RR: 1.27; 95% CI: 1.04, 1.55; P = 0.02) and consent rates (RR: 1.44; 95% CI: 1.11, 1.85; P = 0.006) when an incentive payment was offered to participants. Even a small amount of incentive showed significant improvement in both consent (RR: 1.33; 95% CI: 1.03, 1.73; P = 0.03) and response rates (RR: 1.26; 95% CI: 1.08, 1.47; P = 0.004).

Conclusion: In conclusion, our meta-analysis demonstrated statistically significant increases in the rate of consent and responses from participants when offered even small monetary value incentives. These findings suggest that incentives may be used to reduce the rate of recruitment failure and subsequent study termination. However, further RCTs are needed to establish a critical threshold beyond which incentive amount does not alter response rates further and the types of RCTs in which financial incentives are likely to be effective.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. PRISMA 2020 flow diagram for updated systematic reviews, which included searches of databases, registers, and other sources.
Fig 2
Fig 2. Risk of bias assessment.
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
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
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.
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