the extent to which a measurement tool truly measures the theoretical concept (construct) it is intended to measure. It is demonstrated when relationships among items, domains, or concepts align with pre-specified (a priori) hypotheses about how the measure should relate to other variables, patient characteristics, or outcomes. In other words, construct validity provides evidence that the tool behaves as expected within a given theoretical framework.
Example
A new questionnaire is developed to measure fatigue in people with lupus. To demonstrate construct validity, researchers hypothesize that higher scores on the new tool will correlate strongly with existing validated fatigue scales (convergent validity) and only weakly with unrelated constructs such as joint swelling (discriminant validity). If the results match these hypotheses, it supports the instrument’s construct validity.