What is concurrent validity?

In order to better understand concurrent validity, we should approach construct validity first: Construct validity refers to a test's ability to measure what it claims to measure. For example, does a test for depression (such as Beck's Depression Inventory; a commonly used measure of depressive symptoms) actually measure depressive symptoms? This is an important concept to ensure that our test is targeting the concept that we desire to measure. Concurrent validity is a way to test whether our measure targets the desired concept. It achieves this by comparing the correlations between two different measures. For example, if we had designed a 22-item questionnaire for measuring depressive symptoms, we could compare the scores from the same subject on our measure and another previously established measure, such as Beck's Depression Inventory. If the scores are highly correlated with one another, we can say that this suggests our measure is similar, and can therefore be used to measure depressive symptoms.