Individuals change over time. How can we assess this change?

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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.


We want to increase the reliability of psychological research into (intra)individual change

Reliable Change Index 

For the situation where only a pretest and a posttest score on the outcome variable are available, as well as relevant additional information from a normative population (e.g., the reliability of the test), methods have been developed that can generally be described as follows. From the pretest and posttest scores, which are affected by measurement errors and possibly by effects of testing, and with the help of the additional information, an estimation of the true change is calculated. The ratio of this estimation in the numerator and a suitable standard error in the denominator is then used as a criterion, indicated by the generic name Reliable Change Index (RCI).

Fallibility of several RCIs

The presentation of new RCIs proves to be an ongoing affair. Our publications aim at discussing and comparing the various RCIs from a theoretical point of view. This has led to demonstrating the fallibility of several RCIs proposed in the literature, as well as presenting some adjusted RCIs.