More than 25 baseline characteristics were tested as predictors of recurrent VTE. Data on these characteristics were collected by review of all medical records (inpatient and outpatient) in the community for each subject.18 The characteristics included the following: type of event (PE, DVT, or both); age at incident event; sex; year of incident event; patient location at onset (community, community but hospitalized within the previous 90 days, hospital, or nursing home); body mass index (BMI, calculated as the weight in kilograms divided by the square of the height in meters: weight [kg]/[height (m)]2), categorized as underweight (BMI <20), normal weight (BMI ≥20 and ≤24), overweight (BMI >24 and <30), or obese (BMI ≥30)20; chronic heart disease (congestive heart failure or other heart disease [congenital heart disease, cardiomyopathy, ischemic heart disease, or valvular heart disease]); active malignant neoplasm (excluding nonmelanoma skin cancer) with or without chemotherapy (cytotoxic or immunosuppressive therapy for malignant neoplasm, excluding tamoxifen); serious neurologic disease (stroke or other disease affecting the nervous system with associated extremity paresis, or acute stroke with extremity paresis requiring hospitalization within the previous 3 months); surgery requiring anesthesia (general, orthopedic, neurologic, or gynecologic surgery); anesthesia (general, epidural/spinal, other); trauma requiring hospital admission (major fracture or severe soft-tissue injury); chronic lung disease (chronic obstructive pulmonary disease, emphysema, chronic bronchitis, bronchiectasis, interstitial lung disease, or pulmonary hypertension [asthma was included only if there was documented evidence of fixed airflow obstruction]); chronic liver disease (including active hepatitis within the previous 3 months); chronic renal disease (physician's diagnosis and creatinine level >175 µmol/L [2 mg/dL] for at least 3 months, or nephrotic syndrome); inflammatory bowel disease; previous superficial vein thrombosis; varicose veins (varicose veins or treated varicose veins [injection sclerotherapy or stripping]); central venous catheter or transvenous pacemaker; anticoagulation therapy or prophylaxis immediately preceding or at the time of the incident event; smoking status (none, former, or current [cigarettes only]); hormone therapy (estrogen or progesterone); and (for women only) pregnancy or postpartum (within 3 months of delivery) at the time of the incident event, oral contraceptive use, gynecologic surgery, and tamoxifen therapy. The characteristics related to active malignant neoplasm, chemotherapy, surgery, anesthesia, trauma, hormone therapy, oral contraceptive use, and tamoxifen therapy were recorded as present only if documented within the 3 months prior to the VTE event. All other characteristics were recorded as present if documented any time prior to the incident VTE event. Body mass index calculations were based on the most recent height and weight measurements prior to the incident event. The BMI could not be calculated for 82 cases, mainly because of missing height measurements. For these cases, BMI values were imputed by assigning to each case the average height and/or weight of those incident cases of the same sex and age group. For the one child younger than 15 years with a missing measurement for height, we used the 50th height percentile from the published 1976 National Center for Health Statistics growth chart. Smoking status was based on tobacco use in the 3 months prior to the incident event. Smoking status was missing for 92 patients and was evaluated only after determination of the otherwise final model (including interactions). In the subset of cases with complete smoking information, we verified that the final multivariate model variables did not have hazard ratios differing from those computed using all cases. We then categorized those patients with missing smoking status as nonsmokers, reasoning that this would be the most conservative approach. Because pregnancy and the postpartum period, oral contraceptive use, gynecologic surgery, and tamoxifen therapy could only be evaluated in women, these variables were assessed after determining the otherwise final model, including interactions.