I have a data set with 5 different kinds of nutrient statuses and I want to see whether they are associated with categorical / ordinal grades at school. I have multiple covariates which I will included in the analyses. Due to missing values I have used the multiple imputation strategy (5 times).
So now I have this databases and I want to do a optimal scaling regression (
However when I do this SPSS says:
The following variables have values less than or equal to zero, which are considered as missing in this procedure: Smoking, etc.
Why is this and what can I do about it?