Cost of illness

Cost-of-illness (COI) analysis provides a summary of the total economic burden of a specific disease on society. This encompasses direct costs, such as healthcare system expenditures for diagnosis, treatment, disease management, and patients’ out-of-pocket expenses (e.g. travel, over-the-counter medications), as well as indirect costs, including productivity losses due to work absence. COI studies often estimate resource use from surveys and registries, converting these to costs using representative unit costs and aggregating them across relevant populations. In the US, charges may be used and adjusted with cost-to-charge ratios. COI studies are often used to highlight the large burden associated with particular conditions, as well as differentials by patient and other characteristics. Although such studies can provide useful baseline values for economic evaluations, they are not economic evaluations and they do not estimate how the cost burden might change if new interventions are introduced. Costs attributable to a condition can be estimated by comparing matched groups with and without the condition, though this can be complex for co-occurring conditions, and COI studies have been criticised for potential overestimation of disease-specific costs.