The use of the tetrachoric implies assumption of underlying (unassessed) normal distribution. I don't know if there are cases where the phi would outperform the tetrachoric (or on what standards one would evaluate performance) if the tetrachoic assumptions were wrong, but I would be interested in knowing... bill magee </fontfamily> --Apple-Mail-12-1007479950-- * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/