Available data suggest that prospective research participants may frequently not understand information disclosed to them in the informed consent process. Little is known about how understanding can be improved. To review research on interventions to improve research participants' understanding of information disclosed in the informed consent process. A search of MEDLINE was performed using the terms informed consent and clinical research and informed consent and (comprehension or understanding) from 1966 to March 2004 , which included randomized controlled trials, longitudinal trials, and controlled trials with nonrandom allocation that compared the understanding of research participants who had undergone only a standard informed consent process to that of participants who had received an intervention to improve their understanding. A comprehensive bibliography of empirical research on informed consent published in January 1999 was also reviewed, as were personal files and all issues of the journals IRB and Controlled Clinical Trials. Study design, quality criteria, population characteristics, interventions, and outcomes for each trial were extracted. The statistical significance of the interventions' effects on understanding were noted, as were mean scores for understanding for each group of each trial. For those trials that measured the secondary outcomes of satisfaction and willingness to enroll, results were also summarized. Thirty studies described 42 trials that met inclusion criteria. Of 12 trials of multimedia interventions, 3 showed significant improvement in understanding. Of 15 trials of enhanced consent forms, 6 showed significant improvement in understanding (all P<.05), but 5 of 6 trials were of limited quality, casting doubt on their practical relevance. Of 5 trials of extended discussion, 3 showed significant improvement in understanding (all P<.001) and 2 showed trends toward improvement (P=.054 and P=.08). Of 5 trials of test/feedback, all showed significant improvement in understanding (all P<.05) but were flawed in that they may have mistaken rote memorization for improvement in understanding. Another 5 trials were put into a miscellaneous category and had varying impact on understanding. Some demographic factors, particularly lower education, were associated with less understanding. Satisfaction and willingness to enroll were never significantly diminished by an intervention . Efforts to improve understanding through the use of multimedia and enhanced consent forms have had only limited success. Having a study team member or a neutral educator spend more time talking one-on-one to study participants appears to be the most effective available way of improving research participants' understanding; however, further research is needed.
