Often, researchers are interested in hypothetical constructs. These are constructs that can not be observed directly by empirical evidence. The question arises how to determine whether the measurement of a hypothetical construct (that can not be observed directly) is valid. Chronbach and Meehl say that the validity of the measurement of a hypothetical construct can be determined by comparing the measure with other measures. Scores on an instrument for self-confidence for example should correlate positively with measures for optimism, but negatively with measures for insecurity and fear.

A measurement instrument has construct validity when 1) it correlates strongly with instruments with which it should correlate (convergent validity) and 2) it does not correlate (or correlates to a small extent) with instruments to which it should not correlate (discriminant validity).