On the basis of Ferguson's formula extending the KR-20 formula for use with tests of more than two categories of response, a formula was derived to provide a simple and practical approach to estimating internal consistency. Preliminary try-out indicated a need for adjustment of the formula for those tests which do not obtain a rectangular distribution of responses among categories. The corrected formula was empirically shown to be effective in predicting the Ferguson formula values, while a formula developed by Webster for use with multiple categories of response was not effective.
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