Clinical Trial Participants Compared with Nonparticipants in Cystic Fibrosis

The randomized clinical trial has been an important tool for expanding our knowledge of disease. This study is the first to compare trial participants to the entire eligible population. We performed a cohort analysis using data from the Cystic Fibrosis Foundation Registry database between 1992 and 1998. There were 8,735 patients older than 6 yr followed for the entire period. Of the patients, 2,635 patients (30.2%) were enrolled in at least 1 of 32 Institutional Review Board-approved clinical trials, with an average annual participation rate of 7%. Patients enrolled in clinical trials had more advanced disease as judged by FEV(1)% predicted (68 vs. 77%, p < 0.001), higher rates of Pseudomonas aeruginosa infection (71 vs. 65%, p < 0.01), and were more likely to have private insurance (odds ratio [OR], 1.25; 95% confidence interval [CI], 1.14-1.37) and be white (OR, 1.98; 95% CI, 1.44-2.70). No sex differences were noted. Despite the worse clinical status at baseline, clinical trial participants had a lower average annual rate of decline in lung function (1.33%/yr; 95% CI, 1.20, 1.46; compared with 1.52%; 95% CI, 1.43-1.60). These results show that the overall participation rate is very high. Despite more advanced disease at baseline, lung function decline was lower in trial participants; the cause of this difference is unclear. The differences seen in insurance status are concerning. Efforts should be made to ensure adequate representation from different social demographic groups.