Internal to SERVQUAL. A high level of correlation between SERVQUAL scores and a different, reliable and valid measure of SQ, would indicate a high level of external convergent validity. Discriminant validity is the extent to which a measure does not correlate with other measures from which it is purported to differ. If SQ evaluations were composed of five distinct RATER dimensions, one would expect little correlation between the five factors. SERVQUAL’s dimensionality would be regarded as more stable if individual items loaded on to the dimensions to which they belong.