Solved – Calculate Cronbach’s alpha for polytomous items in R

Question

Does anyone know whether there is a function which can calculate Cronbach's alpha for polytomous items with different categories in R?

Answer 1

As far as I understand, standard alpha() function from the psych package (http://personality-project.org/r/html/alpha.html) is not appropriate here, but I'm not absolutely sure about that. It seems to me that, in order to calculate Cronbach's $\alpha$ in R for mixed data, including polytomous items, you can use either function scoreItems() from the psych package: http://www.personality-project.org/r/html/score.items.html), or function cronbach.alpha() from the Item Response Theory (IRT)-focused package ltm (http://cran.r-project.org/web/packages/ltm).

Other measures of reliability of potential interest include $\lambda$ and $\omega$ (see the "Reliability" paper by Revelle and Condon: https://sapa-project.org/dmc/docs/RCreliability2014.pdf). I have also ran across an interesting open source Shiny-based Web application for IRT models, developed by professor Atsushi Mizumoto: http://spark.rstudio.com/mizumot88/irt. The code uses reliability() function from the classical test theory (CTT)-focused CTT package for calculating Cronbach's $\alpha$.