title: GEE with Gaussian estimation of the correlations when data are incomplete.
abstract: This paper considers a modification of generalized estimating equations (GEE) for handling missing binary response data. The proposed method uses Gaussian estimation of the correlation parameters, i.e., the estimating function that yields an estimate of the correlation parameters is obtained from the multivariate normal likelihood. The proposed method yields consistent estimates of the regression parameters when data are missing completely at random (MCAR). However, when data are missing at random (MAR), consistency may not hold. In a simulation study with repeated binary outcomes that are missing at random, the magnitude of the potential bias that can arise is examined. The results of the simulation study indicate that, when the working correlation matrix is correctly specified, the bias is almost negligible for the modified GEE. In the simulation study, the proposed modification of GEE is also compared to the standard GEE, multiple imputation, and weighted estimating equations approaches. Finally, the proposed method is illustrated using data from a longitudinal clinical trial comparing two therapeutic treatments, zidovudine (AZT) and didanosine (ddI), in patients with HIV.
authors.affiliation: Dana Farber Cancer Institute, Boston, Massachusetts 02115, USA. lipsitzs@musc.edu
authors.forename: S R
authors.initials: SR
authors.lastname: Lipsitz
authors.forename: G
authors.initials: G
authors.lastname: Molenberghs
authors.forename: G M
authors.initials: GM
authors.lastname: Fitzmaurice
authors.forename: J
authors.initials: J
authors.lastname: Ibrahim
mesh_terms: D019380:Anti-HIV Agents / Q000627:therapeutic use; D001699:Biometry / Q000379:methods; D003198:Computer Simulation; D018849:Controlled Clinical Trials as Topic / Q000379:methods; D016049:Didanosine / Q000627:therapeutic use; D015658:HIV Infections / Q000188:drug therapy; D006801:Humans; D008137:Longitudinal Studies; D015233:Models, Statistical; D016011:Normal Distribution; D015215:Zidovudine / Q000627:therapeutic use
chemical_list: D019380:Anti-HIV Agents; D015215:Zidovudine; D016049:Didanosine