1. Johns Hopkins University; Center for Clinical Trials, Bloomberg School of Public Health; Room W5010 615 N. Wolfe St. Baltimore Maryland USA 21205
2. University of Maryland School of Medicine; Epidemiology and Preventive Medicine; 660 West Redwood Street Baltimore Maryland USA 21201-1596
3. German Cochrane Center; Dept. Med. Biometry & Statistics; University Medical Center Stefan-Meier-Str. 26 Freiburg Germany 79104