RT Journal Article SR Electronic T1 Missing covariate data in clinical research: when and when not to use the missing-indicator method for analysis JF Canadian Medical Association Journal JO CMAJ FD Canadian Medical Association SP 1265 OP 1269 DO 10.1503/cmaj.110977 VO 184 IS 11 A1 Groenwold, Rolf H.H. A1 White, Ian R. A1 Donders, A. Rogier T. A1 Carpenter, James R. A1 Altman, Douglas G. A1 Moons, Karel G.M. YR 2012 UL http://www.cmaj.ca/content/184/11/1265.abstract AB