ABSTRACT
This chapter begins by discussing the concept of validity in measurement and identifies criterion validity as central to the assessment and evaluation of clinical problems. The limitations of standardised measures with respect to criterion validity are identified and idiographic measurement is defined and introduced. Several types of idiographic measures are discussed, including self-report and observational measures. The importance of reliability in these measures is highlighted and methods for obtaining reliable observations are given. The chapter highlights the advantage of personal questionnaire methodology for measuring subjective states.
