Identify the true statements about test-retest reliability as a method of calculating the reliability of measures.
a. For very short time intervals, most attributes are quite unstable, and a low test-retest reliability should be expected.
b. It is generally recommended that test-retest reliability be at least 0.90 for a measure to have an acceptable degree of reliability.
c. Higher test-retest reliabilities are indicative of greater measurement stability.
d. It involves calculating correlation based on total test scores or separate correlations for each item.