Statistics in the News: Chapter 17 Multiple Regression and Correlation
Survival of the Fittest
Exercise capacity is known to be an important prognostic factor in patients with cardiovascular disease, but does it predict mortality equally well among healthy persons? Medical researchers recently studied 6,213 men referred for treadmill exercise testing. Subjects were classified into two groups: 3,679 had an abnormal exercise-test result or a history of cardiovascular disease and 2,534 had a normal exercise-test result and no history of cardiovascular disease. Mortality was studied during a mean follow-up period of 6.2 years.
There were 1,256 deaths during the follow-up period. The incidence of death was related to a number of factors, including age, history of smoking, diabetes, total cholesterol level, maximal heart rate, maximal systolic and diastolic blood pressure, and exercise capacity. Absolute peak exercise capacity, measured in metabolic equivalents (MET), was the strongest predictor of the risk of death among both normal subjects and those with cardiovascular disease. (One MET is defined the oxygen consumed when a person is at rest, which is equivalent to 3.5 milliliters of oxygen per kilogram of body weight per minute.) Each 1 MET increase in exercise capacity conferred a 12 percent improvement in survival. Thus, exercise capacity turned out to be a more powerful predictor of mortality among men than other established risk factors for cardiovascular disease.
Crucial results are summarized in Table A
TABLE A Results of a Treadmill Study
Sources: Adapted from Jonathan Myers et al., "Exercise Capacity and Mortality Among Men Referred for Exercise Testing," The New England Journal of Medicine, March 14, 2002, pp. 793-801, and Gary J. Balady, "Survival of the Fittest-More Evidence," ibid., pp. 852-854.