Here are some answers
> I am trying to use SPM 8 to do model comparisons with DCM. I have two questions: 1) do I have to do family inference with this > batch? I want to do model selection in 4 models rather than family comparisons. Is there any way I can do this?
You do not have to create family in this batch. In option family inference, leave 'load family' - empty - just leave it as it is by default. But even if you create a family, you will still get estimation of posterior evidence for the entire model set (in your case 4 models) including model free energy, model expected probability and the exceedance probability of each model.
Though there might be differences in these values per model if you include family inference and if you do not.
>2) I defined two families with model 1 and 3 in family one where there is a connection from STG to MOG and mdoel 2 and 4 in >family two where there is no connection from stg to mog. However, I got an error message saying "invalid family". Can > >anybody help? Thanks.
This error occurs usually if you make a mistake while defining family members. You have to take care not to include the same model twice, and to include each model once - otherwise this error will occur. The other reason might be the format in which you fill in the numbers.