We restricted the analysis to individuals 20 years or older. Individuals with possible DVT were identified by the presence of the following International Classification of Disease, Ninth Revision, Clinical Modification (ICD-9-CM) codes in any inpatient or outpatient diagnosis field: 671.3x, 671.4x, 671.5x, 671.9x, 451.11, 451.19, 451.2, 451.81, 453.2, and 453.9. Pulmonary embolism was identified using ICD-9-CM codes 673.2x, 673.8x, 415.11, and 415.19. Unique identification numbers were used to track individuals over time; therefore, each person with a VTE diagnosis was only counted once, regardless of the number of times the diagnosis was noted. Individuals in the population denominator were also tracked longitudinally and were included if they were enrolled in any health plan, even if no claims were submitted during the 2-year period. The administrative prevalence of VTE was calculated by dividing the number of individuals with a VTE diagnosis during the 2-year study period by the total number of individuals enrolled in health plans during the same period.