The assessment of intra-individual change is an important topic in various fields of psychology, for example in psychotherapy or neuropsychology research. However, pretest and posttest scores used in research on this subject, are affected by measurement errors and effects of testing. In order to clarify those effects, we try to improve the Reliable Change Index (RCI).
Differtent types of change
Research into change may be directed at the assessment of the effects of intentional interventions such as psychotherapy or brain surgery, or unintentional interventions such as sports concussions, or even in the absence of an intervention – for example the effects of aging. The question of whether a group has changed between two assessments is readily answered with the help of current statistical tools. But the question of whether a given person has changed is often more relevant to a practitioner or a researcher.