Dear SAS-Lers,

I could not have made my work without all the help I have got from all of you - unknown friends. When I finish I will make a summary to the list of the most fruitful tips I got.

Until now I have been "kneading" my data set for a long time, thinking I was close to an end. But then a serious question re. missing values turned up:

As some of you already know, I am analyzing a split plot experiment with covariates using PROC MIXED. Now I am wondering how to treat missing values. There are some of them here and there. This question also relate to the treatment of a few extreme outliers, as - if I exclude an outlier - it will appear as a missing value.

The field experiment consist of three blocks (replicates). Eight manuring treatments as main plots within each block. Each main plot is split into two subplots treated and not treated with some preparations. Each subplot is characterized with some measurements which are used as covariates - eventually used as interaction terms with treatments. NOW THE PROBLEM: If I have one missing value in the response variable (i.e. representing a result from one sub plot (a)) how will this be handled by PROC MIXED. As I have understood PROC MIXED will handle this situation. But - now my question - should I exclude the value in the same response variable representing the neighbor subplot (b) within the same main plot? If I do not make that exclusion will the covariate "run away" with the value from the measured subplot (b) without having possibility to account for the missing value from its neighbor (a)? - Or will the keeping of this value (b) make it possible to estimate (a) - which should be the same as letting PROC MIXED take care of the problem?

Looking forward to fruitful comments

torben

::::::::::::::::::::::::::::::::::::::::::::: Torben Haslund Department of Plant Biology Swedish University of Agricultural Sciences P.O. Box 7080 S - 750 07 UPPSALA, Sweden

E-mail address: Torben.Haslund@vbiol.slu.se Home and postal address: Ostre Paradisvej 7B, DK-2840 Holte, Denmark Home phone: +45 4541 1198