What is Construct validity?

Construct validity is the evidence that a test measures the psychological attribute it claims to measure, rather than something merely correlated with it. It is built from convergent evidence — the score tracks other measures of the same attribute — and discriminant evidence, that it does not track measures of different attributes.

Why it is the hard one

Nobody can observe conscientiousness, numerical reasoning or resilience directly. A test is a set of observable behaviours claimed to stand in for an unobservable attribute, and construct validity is the argument that the substitution is sound.

That argument is never settled by a single study. It accumulates: factor structure that reproduces across samples, correlations with related measures that are high, correlations with unrelated measures that are low, and score differences between groups that theory predicted in advance.

How to interrogate a vendor's claim

Ask what the construct is defined as, in one sentence, before asking anything statistical. A great many instruments cannot answer this cleanly, and a construct that cannot be stated cannot be validated.

Then ask for the discriminant evidence specifically. Convergent evidence is easy to produce and is what gets published in marketing material; discriminant evidence — showing the test does not simply measure verbal ability, or reading speed, or willingness to present well — is the part that distinguishes a measured instrument from a plausible questionnaire.

Not the same as face validity

Face validity is whether the test looks right to the person taking it. Construct validity is whether it measures what it says. The two are independent, and a test can have plenty of the first and none of the second.

Face validity