This shiny app will:
– Give you the polychoric (or tetrachoric, in case of binary data) correlation matrix
– Do Parallel Analysis and a scree plot based on the polychoric (or tetrachoric) correlation matrix
– Calculate ordinal alpha as recommended in:
Zumbo, B. D., Gadermann, A. M., & Zeisser, C.. (2007). Ordinal Versions of Coefficients Alpha and Theta For Likert Rating Scales. Journal of Modern Applied Statistical Methods, 6, 21-29.
It currently takes in certain SPSS files (so .sav file extensions from older versions of SPSS, say around 2013 or less), Microsoft Excel files (so .xls file extensions) and comma-delimited files (so .csv extensions). If your data is in none of those files, please change it before using the app (it’s super easy). or it will give you an error. Also notice that the app will use ALL of the variables in the file uploaded, so make sure you upload a file that only has the variables (test items in most cases) which you want to correlate/calculate alpha for. You’ll need to provide a clean dataset for it to work. So if you have missing values, you’ll need to manually remove them before submitting it. If there are outliers, those need to be dealt with before using the app.
Please notice that in accordance to research, if you have 8 (or more) Likert responses, the app will give you an error saying you have enough categories to safely treat your variables as continuous, so you don’t really need to use this app. You can see why in Rhemtulla, Brosseau-Liard & Savalei (2012).