I'm trying to find the correct analysis that will allow me to carry out the equivalent of a repeated measures MANCOVA with a covariate that varies over three conditions. Basically I have an experiment with 3 different types of task where every participant does every task in a randomised order. I'm measuring the effect of these tasks on a bunch of mood measures. BUT I've found out that one of the tasks was significantly more difficult than the other two. I think this means I need to make task difficulty a covariate, however it is not constant over the three conditions.

Does anyone know what kind of analysis I should be running, and how I should be setting my data up (wide or long form). Is it some kind of mixed modelling (of which I know very little)? Bonus points if it can be done using SPSS.

Much thanks to anyone who answers,

Kellie