Defining and assessing test reliability and validity
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Reliability refers to the consistency of a test in measuring the intended construct. A test-retest method is used to determine reliability by administering the same test twice to students and computing a rank correlation coefficient, such as the Spearman Rho, based on comparing the rank orders of student scores between the two test administrations. The example shows student scores from an initial (FA) and subsequent (SA) administration of a test, with their ranks and the differences between ranks used to calculate the standard deviation.
Defining and assessing test reliability and validity
- 2. RELIABILITY refers to the consistency of a test in measuring whatever it measures. It is the degree to which a test will yield similar or comparable results for the same students when administered at different times. This is usually measured through the computation of a reliability coefficient.
- 3. TEST RETEST METHOD Test reliability is determined from the repetition of the same test. Thus, a test is administered twice. Scores obtained by the students in both test administration are rank ordered and a rank correlation coefficient is obtained with the use of Spearman Rho.
- 4. STUDENT SCORES FA SCORES - SA 1 33 29 2 28 26 3 44 42 4 36 30 5 26 28 6 35 35 7 42 39 8 40 41 9 20 20 10 28 28
- 5. Ss-FA X Ss-SA Y RANK X RANK Y D D 33 29 6 7 1 1 28 26 7.5 10 -2.5 6.25 44 42 1 1 0 0 36 30 4 6 -2 4 26 28 9 8.5 0.5 0.25 35 35 5 5 0 0 42 39 2 4 -2 4 20 40 10 3 7 49 28 28 7.5 8.5 -1 1 SD2 = 62.5