RE: Coding for missing data values

From: "Bachman, William (MYD)" bachmanw@iconus.com Subject: RE: [NMusers] Coding for missing data values Date: Mon, June 28, 2004 12:20 pm There are a number of ways you can do this: 1. simply code separate parameters for those with and without the covariate. IF(TECL.EQ.0) THEN CL=THETA(1) ;where TECL is assigned to zero in the data file for those with missing value ELSE CL=THETA(2)+(TECL-5.4)*THETA(3) ; where 5.4 might be the mean TECL ENDIF 2. impute the missing covariate. again a number of ways this can be done. eg. simplest way is to use the population mean for the missing subjects or devise a more complex imputation scheme possibly based on the relationship between the covariate and other available covariates. second way probably more prone to inducing bias in the model, first way possibly less explanatory of variance. William J. Bachman, Ph.D. Manager, Pharmacometrics Research and Development GloboMax The Strategic Pharmaceutical Development Division of ICON plc 7250 Parkway Drive, Suite 430 Hanover, MD 21076 410-782-2212 bachmanw@iconus.com