I would like to create a composite scale for different attitudes by calculating the mean score from different items on a questionnaire. Most of the items use Likert scales however some of the items on the questionnaire just use yes/no answers. Is it still possible to combine these scores to create a composite scale? How would I do this?
e.g.
Question 1 Likert scale 1-5
Question 9 Yes/No
Best Answer
You can do this, but taking the simple mean is not good anymore because of different scales. You can do factor analysis to get at the "latent construct" you are trying to evaluate, or principal components for pure data reduction. There's been work on doing these with a mix of variable types.