In psychology, a construct is a phenomenon or a variable in a model that is not directly observable or measurable - intelligence is a classic example. Psychologists use surveys and tests as proxies to measure the variable, and require some confirmation that what they are testing or surveying is, in fact, the underlying phenomenon. This congruence is measured by construct validity - specifically by "convergent construct validity." Practical work with the survey or test is required before this can be done. A related idea metric is divergent or discriminant validity, where the purpose is to determine whether the instrument is measuring something different from the phenomenon in question.