Alpha reliabilities are the standard approach for summated scales built from grouped-ordinal or continuous items. A variation (KR-20) (Kuder-Richardson's formula) can be used with dichotomous items.

Hi Geoffrey,

Please find attached an explanation of Cronbach's alpha. This article explains its use very well.

Mark

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2792363/

Hi Geoffrey, all the variables must be in the same scale, i.e all categorical, or all continuous. That is not your case. However Subhashisa's steps are helpful

Thanks for all your help