Determination of vital status at the end of the DIG trial

The Digitalis Investigation Group (DIG) trial was a randomized, double-blind placebo-controlled trial whose primary objective was to determine whether digoxin had beneficial, harmful, or no effect on total mortality in patients with heart failure who were in sinus rhythm and whose ejection fraction was ⩽0.45. The study was designed as a large simple trial with a large number of centers (302) in the United States and Canada, many of which were inexperienced in research. To ensure that the results of the trial would be reported accurately without possible bias due to missing data, the study leadership decided that no outcome results would be reported until the vital status at the end of the study was known for at least 97% of the study participants. Planning for closeout of the study began a year prior to the common end date of December 31, 1995 and included plans for obtaining vital status on December 31, 1995. Participants were given postcards at their final study visit to be completed and mailed on or after January 1, 1996. Of 5602 postcards distributed, 5070 (90.5%) were completed and returned. A contract search agency was hired to locate the remaining participants. Of the total 7788 participants entered into the DIG trial, only 97 participants (1.2%) could not have their vital status as of December 31, 1995 determined. It is recommended that investigators having an outcome measure with a common end date include plans in their protocols for obtaining their measures and activate those plans as early as possible during the course of the study.