APA Dictionary of Psychology

in the application of factor analysis to personality, various types of information collected on individuals and classified according to the information source. For example, Q data are collected on individuals from self-report questionnaires and inventories, and T data are acquired about individuals from the results of a formal scientific measurement or objective test. Other types include L data, or information gathered from individual life histories, and O data, or information gathered about individuals from other people (e.g., family members). [first specified by Raymond B. Cattell]