['To define how much regression to the mean confounds apparent responsiveness in subgroup analyses, and to test, using techniques that remove regression to the mean, whether hypercholesterolemic subjects are more likely to respond to diet.', 'Data collected on 812 men and women participating in the Minnesota Coronary Survey Dietary Trial who had at least 2 total cholesterol measurements on a high-saturated-fat diet and 1 cholesterol measurement on a low-saturated-fat diet were analyzed for the effects of initial serum cholesterol and regression toward the mean on measurement of diet responsiveness.', 'If regression towards the mean is not taken into account, dietary responsiveness in patients with mean cholesterol levels of 280 mg/dL was -25%, whereas dietary responsiveness in subjects with mean serum cholesterol levels of 156 mg/dL was -5%. After regression toward the mean was taken into account, subjects with high initial serum cholesterol levels had an 18% reduction in serum cholesterol levels whereas subjects with lower levels had an 11% reduction. Even after regression toward the mean is accounted for, subjects with high serum cholesterol levels were significantly more diet-responsive (p < 0.005).'] Is response to a cholesterol-lowering diet : efficacy greater in hypercholesterolemic subjects even after adjustment for regression to the mean?