Theorizing about causes at the individual level while estimating effects at the population level: implications for prevention.

The dominant philosophy of modern epidemiology is individualism, despite the limitations of epidemiologic tools and methods when considering the individual level. We pursue information on increasingly reductionist causes in our search for knowledge of causes of specific cases. Philosophical reasoning and empiric evidence suggest that this search may not be as fruitful as proponents claim. I argue that using individualism to guide our search for causes of disease hinders our effectiveness in contributing to disease prevention, because the positive predictive values of most established genetic and environmental risk factors for noninfectious diseases are too low to be quantitatively convincing to an individual.