test-retest reliability-a test's reliability that is established by administering the same test twice to a group of test-takers. The correlation between the two scores earned by test-takers on each testing occassion indicates whether the test is measuring consistently.
alternate-forms reliability-a measure of a test's reliability established by administering two forms of the test to test-takers.
spit-half reliability-a measure of a test's reliability established by correlating the scores for half the items on the test with the scores on the other half of the test items.
coefficient alpha-the average of all posible split-half reliabilities for a given test