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Analyze Assessment

Analyzing Test Results

Discrimination Index (DI) This assesses high-scoring and low-scoring student responses to test items. An acceptable level for this is 25%. It is calculated by considering the top percent and bottom percent of the student scores as follows: DI= a-b. a=response freq from top scoring students on an item. b= response freq from low scoring students on an item.
Point Biserial Index (PBI) or Point Biserial Correlation Coefficient This ranges from -1.00 to 1.00. Positive for the correct answer indicates that high-scoring students answered a test item correctly more frequently than low-scoring students and a negative indicates that low-scoring students answered a test item correctly more frequently than high-scoring students.
Kuder-Richardson Formula 20 (KR-20) This assesses consistency and reliability and may be used to measure interitem consistency. The ranges from -1.0 and 1.0, where reliability coefficient of 1.0 indicates perfect reliability and a reliability coefficient of 0.0 indicates that the test lacks reliability.