Do the effects of major risk factors for mortality rise or fall with age?
Researchers are often interested in how a risk factor's effect on mortality changes with age because the pattern has direct relevancies to life-course theories, public health practice, and demographic modeling. Here we highlight the importance of mathematical scale to interpreting risk factor by age interactions, describing how the choice of scale has critical implications for theory development and arguing that many life-course studies have not recognized the importance of scale to conclusions drawn from their findings. We also provide an empirical analysis of risk factor by age interactions drawing from a set of major risk factors for mortality often studied in demography and epidemiology. We show that these risk factors conform to a general pattern-the strength of their association with mortality tends to increase with age. This prevailing pattern of increasing risks by age across multiple major risk factors for mortality has not been identified previously. We go on to argue that the pattern has critical underpinnings for life-course theory, public health allocation, and clinical practice.