LXR Software Support
We Stand Corrected
Correction Date: November 13th 2008 - LXR*TEST User Guide
Appendix A Test Reliability
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test reliability
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A measure of how reliable a test is in differentiating student achievement. LXR*TEST
calculates test reliability using the Cronbach-Alpha formula (also known as the
coefficient alpha formula). The formula used is:
where:
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a
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coefficient alpha (estimated internal consistency reliability)
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b
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total number of questions on test
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or
where:
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n
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number of students
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tj
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test score for each student
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j
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a particular student
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t
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test mean
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Xij
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student's score on a question
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Xi
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item mean
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Correction Date: August 21st 2009 - LXR*TEST User Guide
Appendix A Point-biserial
In some of the older user guides, the Y
1 - Y was written as Y
1 - Y
2.
The image below shows the correct formula.
