IMPUTE: Re: MNAR or MAR ?

[Craig Newgard]

Julien, What you describe does not sound like it would fit the MAR or MCAR assumptions required.  When you have reason to suspect that one group within a sample (e.g., fathers) is different than other groups within a sample (e.g., mothers, children), then you may think about performing MI separately on the groups, then re-combining the data.  The ability to do this is at least partially contingent on having sufficient data within each group to build a MI model.   Craig     Craig D. Newgard, MD, MPH Assistant Professor Department of Emergency Medicine Department of Public Health & Preventative Medicine Oregon Health & Science University 3181 Sam Jackson Park Road Mail Code CR-114 Portland, OR 97201-3098 (503) 494-1668 (Office) (503) 494-4640 (Fax) [EMAIL PROTECTED] >>> Julien Bois <[EMAIL PROTECTED]> 08/21/03 12:48AM >>> Hi all Here is a (maybe) simple question as I am new in using imputation methods. My question does not deal with very sharp statistical techniques, rather it concerns the core sense of this method. I do studies with families and I usually get data from fathers, mothers and children. Most often data from fathers is missing because of divorced families or fathers who don't want to complete questionnaires. In other words when data from fathers is missing, all the answers are missing and not only few items. Then imagine a simple design with only one wave of data collected. If I want to use data from both fathers, mothers and children, I have to limit my sample to complete families which can be seen as using a listwise deletion. But if I use an imputation method in order to enhance the sample size, I am likely to generate data for fathers from nothing because most often they don't answer AT ALL to the questionnaire. How that kind of data can be described ? Are they MAR or MNAR ? In this case is imputation required and does it works reasonnably well ? Does it exists special methods of imputation for that kind of situations that are easily available ? Does anyone has a reference on this topic ? Any help is appreciated. Julien BOIS Julien Laboratoire Sport et Environnement Social Universit� Joseph Fourier 38400 Saint Martin d'H�res FRANCE 00 (33) (0)4 76 63 50 97 mailto : [EMAIL PROTECTED] Site Web : http://www.ujf-grenoble.fr/ufraps/Recherche/SENS/Membres/Page_Bois.htm