Hi, I was looking at a coding example in Ramon Littel's book 'SAS for Mixed Modells', where he is looking at an interaction between a continuous (hour) and a categorical (drug) variable in the contrast statment. I don't understand why (within each contrast) he first specifies the main effect, e.g. "drug 1 -1 0" before specifying the drug*hour interaction. What is the purpose of this? Here is another example of someone doing the same thing in an estimate statement (source: SAS Library: How do I handle interactions of continuous and categorical variables?😞 Can anyone shed some light on why this is necessary, i.e. why the contrast/estimate statments don't just simply contain the interaction of interest, without the main effect? ... View more

The problem: In PROC MIXED, I defined several classes under 'class'. One of them, called 'Status', has two levels, coded as '1' and '2' (i.e. the column for these data consists of ones and twos). When I run the program, the output states that the class 'Status' has one level, and that it's value is '2' This happens even though I have several other classes with two levels coded as '1' and '2', (i.e., as for Status, the data are columns of ones and twos), for which the output correctly states that each of these classes has two levels, with the values '1' and '2'. Anyone know how I can fix this? PS: The data come from an Excel file, which I opened in SPSS and then saved with the .sas7bdat extension PPS: I've already tried removing the entire 'Status' column in Excel and rewriting it. I've also tried coding the levels as letters (e.g. 'C' and 'P'), but the problem remains. ... View more