Venous thromboembolism affects 2-3 per 1000 men and women annually, with a case fatality rate of around 10%, and it results in post-thrombotic syndrome in about a quarter of patients. After anticoagulant treatment is stopped, venous thromboembolism often recurs, with reported cumulative incidences ranging from 19% to 30% in cohorts followed for two to eight years.1 2 Vitamin K antagonists reduce the risk of recurrent venous thromboembolism by more than 80% but also cause major bleeding in a substantial number of patients on long term treatment.3 Thus, the optimum duration of anticoagulant treatment after an episode of venous thromboembolism remains uncertain, despite many trials that have compared different lengths of treatment⇑.

In the linked meta-analysis of individual participants’ data (doi:10.1136/bmj.d3036), Boutitie and colleagues compare outcomes after different lengths of anticoagulant treatment.4 An advantage of this individual patients’ data approach over meta-analysis on a study level is that …