Plan for ascertaining outcome events: Signs or symptoms of all (major and minor) bleeding and thrombosis will be sought at each clinic visit or telephone call. If bleeding or thrombosis is reported, all available objective documentation such as hospital records, transfusion records or results of diagnostic or therapeutic investigations (such as endoscopy) will be obtained. Minor bleeding will frequently not have led to medical evaluation; in cases where minor bleeding is reported the specific setting, nature, duration and required actions will be sought for each event reported by the patient.