The gap between theory and research in delinquency is most evident when one attempts to discuss the questions raised under the heading, concepts and indicators. Concepts belong to the domain of the theorist, indicators to the domain of the researcher. The researcher starting with a theory possesses a set of concepts that are related to each other by propositions or hypotheses. In both cases, the assumption of a one-to-one correspondence between concepts and indicators replaces the one-to-many or many-to-one correspondence between concepts and indicators assumed by those testing a theory and by those interpreting a set of data. Despite the great importance of the procedures for moving from concepts to indicators and from indicators to concepts, precise rules for bridging this gap do not exist. If a measure makes sense as an indicator of a concept, it may be said to have logical validity. Delinquency researchers usually ignore the problem of validity.