Reliability of a Composite Scale
Calculates Cronbach's alpha and standardized alpha (lower bounds on reliability) for a composite (summated-rating) scale. Standardized alpha is for the sum of the standardized items. In addition, the function calculates alpha and standardized alpha for the scale with each item deleted in turn, and computes the correlation between each item and the sum of the other items.
- the covariance matrix of the items
- The function does not return a useful value; it is called for its side effect -- to print the results.
N. Cliff (1986) Psychological testing theory. Pp. 343--349 in S. Kotz and N. Johnson, eds., Encyclopedia of Statistical Sciences, Vol. 7. Wiley.