There is an updated version of the EPV-calculator found here: https://infovoice.se/epv-calculator/
Covariation estimates how different variables relate to each other. The two main purposes are either to investigate how well different variables measure the same thing (Agreements) or, how well variables measuring different things relate to each other (Associations and predictions).
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References
(This section is still under construction. Sorry for the inconvenience.)