Computing Total Attitude Scores

I am studying attitudes towards mental illness and whether they can be changed after an intervention. I will be using a mixed anova to calculate my results, however in order to do so i need to have a total attitude score (i think).

My attitude questionnaire consists of a measure of knowledge, stereotypes and social distance, all with differing scales.
Would i compute an attitude score for each section of my questionnaire and then combine it?

Would really appreciate the help,thanks!
I have a few questions to ask before giving some advice-

1. is this an instrument you designed or a pre-existing survey?
2. what is your sample size?

The reason I ask is because what it sounds like you want to do is a simultaneous equation model. Don't let that worry you if its something you have not done. If you can do a regression or an anova, you can do an SEM :).