Missing covariate data in clinical research: When and when not to use the missing-indicator method for analysis

Groenwold, R. H. H., White, I. R., Donders, A. R. T., Carpenter, J. R., Altman, D. G., & Moons, K. G. M. (2012). Missing covariate data in clinical research: When and when not to use the missing-indicator method for analysis. CMAJ. Canadian Medical Association Journal, 184(11), 1265–1269. https://doi.org/10.1503/cmaj.110977