Title : Regression Analysis with Missing Covariate Data Using Estimating Equations
Author : Lue Ping Zhao, Stuart Lipsitz and Danika Lew
Biometrics
Vol. 52, No. 4 (Dec., 1996), pp. 1165-1182 
(article consists of 18 pages)
Title : Kernel-Based Density Estimates from Incomplete Data
Author : D. M. Titterington and G. M. Mill
Journal of the Royal Statistical Society. Series B (Methodological)
Vol. 45, No. 2 (1983), pp. 258-266 
(article consists of 9 pages)