# What is the correct use of Cronbach's alpha?

I am trying to use Cronbach's alpha in order to see if some variables are measuring the "same", but I have some doubts about the correct use:

1. Can I compute alpha for numerical, ordinal or dichotomous variables? If it is correct to do that, then may I mix dichotomous, ordinal and numerical variables?

2. If Cronbach's alpha cannot be used for numerical, should I turn these variables into ordinal, or not?

3. If all my variables are ordinal, do they have to be on the same scale? I mean if variable 1 goes from 1 to 5, and variable 2 goes from 1 to 3, may I use Cronbach's alpha for these 2 variables?