The Direct Expenditures and Indirect Costs Associated with Treating Asthma in the United States

Historically, COI was based on one of two types of costs, total cost or incremental cost. Total costs provide estimates of the total healthcare expenditure of patients diagnosed with a disease. Incremental cost includes healthcare expenditures solely attributable to the disease. The Sum All Medical and Sum Diagnostic methods are used for the total cost approach. These methods add all costs of the patients diagnosed with disease irrespective of whether or not the costs directly related to disease. The Sum Diagnosis method, adds up the expenditures directly related to the primary diagnosis of the disease. The Matched Control and Regression are the methods used for the incremental approach. Only the incremental approach uses a control group without disease [18]. The Matched Control method calculates the average sum of all medical costs among patients with the disease and subtracts the average sum of all medical costs among similar patients without the disease. The matched control method isolates disease-specific costs by subtracting the costs of control group from the case group, using a matching algorithm to adjust for confounders. In observational studies, the ”treatment”groups (or ”exposure” groups) often exhibit imbalance on covariates. This covariate imbalance is confounded with treatments: It is difficult to attribute differences in responses to the ”treatment” or ”exposure” because the covariates are also believed to influence the response. In research studies, a researcher gets two opportunities to control the covariates. One is at the design level, and other is at the data analysis stage.