A Note on the Standard Length of a Test
- Author(s):
- Myers, Charles T.
- Publication Year:
- 1961
- Report Number:
- RB-61-03
- Source:
- ETS Research Bulletin
- Document Type:
- Report
- Page Count:
- 13
- Subject/Key Words:
- Item Analysis, Test Construction, Test Length, Test Reliability
Abstract
The "standard length" of a test is shown to be N = u/c = (v-c)1C where N = the number of typical items that would have a test reliability of .50; u = the average "error" variance in the test items; c = the average inter-item covariance which is also considered to be equal to the "true" variance of the items; and v = the average item variance. Various methods of computing the necessary data from the item-analysis coefficients are shown.
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- http://dx.doi.org/10.1002/j.2333-8504.1961.tb00104.x