The stability of an instrument is the extent to which similar results are obtained on two separate occasions.
Assessments of an instrument’s stability involve procedures that evaluate test – retest reliability.
e.g. Administer the same measure to a sample twice and then compare the scores by computing a reliability coefficient, which is an index of the magnitude of the test’s reliability. Statistical analysis is correlation –coefficient.
Calculate the Content Validity index,(CVI) Experts rate items on a 4 – point scale of relevance, the item(I) CVI is computed as the number of raters giving a rating of either 3 or 4 , divided by the number of experts.I-CVI of .80 is considered an acceptable value.
Concurrent Validity refers to a measurement device’s ability to vary directly with a measure of the same construct or indirectly with a measure of an opposite construct. It allows you to show that your test is valid by comparing it with an already valid test.