EVALUATING CHOLESTEROL SCREENING - THE IMPORTANCE OF CONTROLLING FOR REGRESSION TO THE MEAN

Objectives: To determine the overall impact of a voluntary cholesterol screening program and to assess the importance of controlling for reg ression to the mean when evaluating the impact on higher-risk subgroup s. Design: Longitudinal study comparing baseline survey and cholestero l results with those obtained 17 months later, with adjustment for reg ression to the mean. Setting: Participants were seen at three sites: a n academic teaching hospital, an intermediate-care hospital, and a sub urban community center. Participants: One thousand fifty-three partici pants were enrolled in a voluntary cholesterol screening program. Meas urements/Main Results: Of 1053 study enrollees, 785 (75%) completed a follow-up questionnaire and 656 (62%) returned for follow-up cholester ol tests. Among all participants at high risk, measured cholesterol le vels were 0.66 mmol/L (25.5 mg/dL) lower at follow-up, but 58% of this apparent change (0.38 mmol/L [14.7 mg/dL]) was attributable to the st atistical phenomenon of regression to the mean. Among all participants at increased (both high and moderate) risk, after controlling for reg ression to the mean, reductions in cholesterol levels were significant for those younger than 60 years (-0.28 mmol/L [-10.8 mg/dL]; 95% conf idence interval, -0.43 to -0.13; n=390) but not for those 60 years or older (+0.007 mmol/L [+0.3 mg/dL]; 95% confidence interval, -0.16 to 0.17; n=266). Conclusions: For subjects found at high risk in a choles terol screening program, more than half of the apparent beneficial cha nge in cholesterol level is attributable to regression to the mean. Fo r participants older than 60 years, no clear benefit of cholesterol sc reening was documented.