Reliability relates to the generalizability, consistency, and stability of a test.
Accounting for Test ErrorOne reason for obtaining a reliability coefficient is to estimate the amount of error that is associated with either test-retest or split-half reliability. We know that any two administrations of a test frequently result in different scores. How can we take that into account when we only test a student once? There are two ways:
100 + [.90 * (75-100)] = 77.5
If you want a 95% confidence interval, you multiply the SEM by +1.96 and -1.96. Add and subtract those values to and from the estimated true score.
Estimated true score = 77.5
68% confidence interval = 77.5 +/- 3 = 74.5 - 80.5
Pearson's Product-Moment Correlation Coefficient