Statistical analysis. Baseline differences between groups will be assessed by the chi-square test (Yates’ correction) for categorical variables and t-test or Mann-Withney U test for continuous variables, as appropriate. Data will be analyzed on intention-to-treat basis. Kaplan-Meier survival curves are plotted to estimate the cumulative incidence of symptomatic recurrent venous thromboembolism and major bleeding. Patients who during the study will develop clinical conditions interfering with the study outcomes (such as ischemic heart disease, cancer, stroke, superficial vein thrombosis, etc) and left the assigned group will be regularly followed-up and included in analysis. Hazard ratios and their 95 percent confidence intervals will be calculated using the Cox’s proportional hazards model. The data will be analyzed using the Prism statistical software package (Version 3.0, GraphPad Software Incorporated, San Diego, CA) and the SPSS statistical package (Version 14.0, SPSS Inc., Chicago, IL).