Greenland S, Finkle WD. A critical look at methods for handling missing covariates in epidemiologic regression analyses. Am J Epidemiol 1995;142:1255-64.
Ranstam J, Turkiewicz A, Boonen S, van Meirhaeghe J, Bastian L, Wardlaw D. Alternative analyses for handling incomplete follow-up in the intention-to-treat analysis: the randomized controlled trial of balloon kyphoplasty versus non-surgical care for vertebral compression fracture (FREE). BMC Medical Research Methodology 2012, 12:35 (24 March 2012).
Saha CK and Jones MP. Bias in the last observation carried forward method under informative dropout. Journal of Statistical Planning and Inference, 139:246-255, 2009.
Vach W, Blettner M. Biased estimation of the odds ratio in case-control studies due to the use of ad hoc methods or correcting for missing values of confounding variables. Am J Epidemiol 1991;134:895-907.