L. Forrow et al., EVALUATING CHOLESTEROL SCREENING - THE IMPORTANCE OF CONTROLLING FOR REGRESSION TO THE MEAN, Archives of internal medicine, 155(20), 1995, pp. 2177-2184
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.