Reliability and validity are both very important criteria for analyzing the quality of measures. Although they are independent aspects, they are also somewhat related. A measurement procedure cannot be valid unless it’s reliable; however, a measurement can be reliable without being valid. There are several ways to measure reliability. Test-retest reliability involves re-running the study multiple times and checking the correlation between results. If the results are consistent, the test is reliable. Split-half reliability is similar; half of the data are selected at random and compared to the other half. If the measure is reliable, the two halves will be quite similar. There is no quantitative measure of validity. Instead, validity is typically gauged by discussing the measure with experts, considering in close detail how the measure relates to the hypothesis, and comparing the results with other tests designed to measure the same outcome.