A Cochrane review included 14 cohort studies with a total of 587 always users and 276 never users. The cohorts of always users yielded an HIV incidence estimate of 1.14 (95% CI 0.56 to 2.04) per 100 person-years, and the cohorts of never users consisting mainly of studies of partners of hemophiliac and transfuion patients yielded an HIV incidence estimate of 5.75 per 100 person-years. The proportionate reduction in HIV seroconversion with condom use was approximately 80%.
Comment: The quality of evidence is upgraded by large magnitude of effect.