Obtaining written informed consent from participants before enrolment in a study is essential. A previous study showed that only 50% of the participants in clinical trials understood the components of informed consent, and the methods of participants’ understanding of informed consent were controversial. This updated meta-analysis aimed to estimate the proportion of participants in clinical trials who understand the different informed consent components. PubMed, EMBASE, the Cochrane Library, and Scopus were searched till April 2023. Therapeutic misconception, ability to name one risk, knowing that treatments were being compared, and understanding the nature of the study, the purpose of the study, the risks and side-effects, the direct benefits, placebo, randomization, voluntariness, freedom to withdraw, the availability of alternative treatment if withdrawn from the trial, confidentiality, compensation, or comprehension were evaluated. This meta-analysis included 117 studies (155 datasets; 22,118 participants). The understanding of the risks and side-effects was investigated in the largest number of studies (n = 100), whereas comparehension was investigated in the smallest number (n = 11). The highest proportions were 97.5%(95% confidence interval (CI): 97.1–97.9) for confidentiality, 95.9% (95% confidence interval (CI): 95.4–96.4) for compensation, 91.4% (95% CI: 90.7–92.1) for the nature of study, 68.1% (95% CI: 51.6–84.6) for knowing that treatments were being compared, and 67.3% (95% CI: 56.6–78) for voluntary nature of participants. The smallest proportions were the concept of placebo (4.8%, 95%CI: 4.4–5.2) and randomization(39.4%, 95%CI: 38.3–40.4). Our findings suggested that most participants understood the fundamental components of informed consent (study confidentiality, nature, compensation, voluntariness, and freedom to withdraw). The understanding of other components, such as placebo and randomization was less satisfactory.
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