Construct validity

Construct validity refers to the evidence that supports pre-defined hypotheses about the expected relationships between a patient-reported outcome measure (PROM) and other measures assessing similar or dissimilar constructs. It encompasses two main types:

1. Convergent validity: This is demonstrated when the outcomes of a PROM show a strong positive correlation with the outcomes of other instruments that measure the same or conceptually related constructs. For example, a high score on the EQ-5D utility index would be expected to correlate with a high score on the SF-36 utility index.
2. Discriminant validity: This is established when a PROM shows a weak or negative correlation with the outcomes of instruments that measure theoretically unrelated constructs. For instance, scores on an introversion scale should exhibit a negative correlation with scores on an extroversion scale.