Fisher’s correlation transformation is commonly used to draw inferences regarding the reliability of tests comprised of dichotomous or polytomous items. It is illustrated theoretically and empirically that omitting test length and difficulty results in inflated Type I error. An empirically unbiased correction is introduced within the transformation that is applicable under any test conditions.
Harring, Jeffrey R. and Wasko, John A.
"Probabilistic Inferences for the Sample Pearson Product Moment Correlation,"
Journal of Modern Applied Statistical Methods: Vol. 10
, Article 8.
Available at: http://digitalcommons.wayne.edu/jmasm/vol10/iss2/8