Invited Commentary Invited Commentary: Beyond Frequencies and Coefficients—Toward Meaningful Descriptions for Life Course Epidemiology

The expected doubling of the elderly population in the United States by year 2030 poses a major challenge to pub-lic health and medical care systems because of limited and progressive diminution of resources for public health and medical care for the elderly (1). This challenge highlights the urgent need for effective programs and policies aimed at the prevention of diseases and maintenance of health over the life span of individuals. Such programs must rely on solid, translatable evidence from population-based etiologic studies. However, both etiologic studies of healthy aging and the translation of study findings into programs and pol-icies are exceedingly complex. For example, to identify accurately and precisely the predictors of the onset and the progression of diseases and functional decline, we must contend with not only 1) multiple arrays of time-varyin