Clinical trial participants compared with nonparticipants in cystic fibrosis

Rationale: 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. Methods: We performed a cohort analysis using data from the Cystic Fibrosis Foundation Registry database between 1992 and 1998. Measurements and Main Results: 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 I 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 FEV1% 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 [Cl], 1.14-1.37) and be white (OR, 1.98; 95% Cl, 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% Cl, 1.20, 1.46; compared with 1.52%; 95% Cl, 1.43-1.60). Conclusions: 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.