Mean inter-item correlation for that alpha and k


        

          This incredibly basic shiny app uses the equation for a standardised Cronbach alpha
          to get a mean inter-item correlation that would have given that alpha, given k, the number of items in the measure.
        

        
 

        
The formula for standardised alpha is:

        
 

        $$\alpha = \frac{kr}{1 +(k-1)r}$$
        
        
 

        

          where r is the mean inter-item correlation.So by rearranging that (boy am I getting rusty at elementary algebra!) 
          the formula to get r given k and alpha is: 
        

        $$\frac{1}{(1 + \frac{k}{\alpha}-\alpha)}$$
        
        

          App created by Chris Evans
          PSYCTC.org
          26.vi.25, updated with cosmetic tweaks 27.vi.25.  Licenced under a 
          Creative Commons, Attribution Licence-ShareAlike
           Please respect that and put an acknowledgement and link back to here if re-using anything from here.
        

        

        


  
Background and related resources

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