Rigorous idiography: Exploring subjective and idiographic data with rigorous methods—The method of derangements

Psychological research often seeks general rules applying across individuals, an aim that is in tension with examining that which is unique to any individual. There are general statistical regularities across individuals’ subjective self-report which enable much psychology and psychotherapy research to combine data from self-report questionnaire responses with statistical and psychometric methods to create a fundamental part of Cronbach and Meehl’s foundational nomological networks of validity. However, these methods only apply when most participants answer the same questions on measures creating nomothetic data and this has led to a neglect of idiographic data. This paper reviews a method of analysis of idiographic data, of “rigorous idiography”: the method of derangements. This is a remarkably simple statistical test of whether purely idiographic data convey reliable information. We show how the method appeared to become stuck in a bibliometric backwater but we expand on its potential for research and practise and hope it will be taken up and used correctly and more widely.