Burden of Disease Attributable to Risk Factors
Mathers and others (2002) describe two traditions for the causal attribution of health outcomes or states: categorical attribution and counterfactual analysis. In categorical attribution, an event such as death is attributed to a single cause, such as a disease or a risk factor, or to a group of causes, according to a defined set of rules such as the International Classification of Diseases (ICD) system (WHO 1992). In counterfactual analysis, the effects of one or a group of diseases or risk factors is estimated by comparing the current or future disease burden with the levels that would be expected under some alternative hypothetical scenario, referred to as the counterfactual, including the absence of or reduction in the diseases or risk factors of interest (see Maldonado and Greenland 2002 for a discussion of the conceptual and methodological issues involved in the use of counterfactuals). In theory, causal attribution of the burden of disease to risk factors can be done using both categorical and counterfactual approaches. For example, researchers have used categorical attribution for attributing diseases and injuries to occupational risk factors in occupational health registries (Leigh and others 1999) and motor vehicle accidents to alcohol use. However, categorical attribution to risk factors overlooks that many diseases have multiple causes (Rothman 1976).
The CRA estimates of the burden of disease and injuries due to risk factors are based on a counterfactual exposure distribution that would result in the lowest population risk, irrespective of whether currently attainable in practice, referred to as the theoretical-minimum-risk exposure distribution (Murray and Lopez 1999). Using the theoretical-minimum-risk exposure distribution as the counterfactual has the advantage of providing an indication of potential gains in population health from reducing the risk from all levels of suboptimal exposure in a consistent way across risk factors.
