The strategies we followed for subjects' enrollment described above were derived from a series of pilot studies we conducted before officially beginning the EAGLE field activities. Because determinants of participation in cases (medical condition, performance status) are different from the determinants in controls (altruism, time), we were concerned that lack of participation might affect estimates of genetic or environmental main effects and interactions on lung cancer risk [10-12]. We made concerted efforts to maximize participation of both cases and controls, and used several strategies and incentives to increase the participation rate in controls.
