Reliable change indices for 16 neuropsychological tests at six different time points

Introduction

Neuropsychological assessment often involves repeated testing in order to assess a cognitive change or conduct a longitudinal follow-up study of a patient. To assess whether the change between assessments is relevant or not, longitudinal reference data are needed. The aim of this study is to provide reference data to enable interpretation of score changes between assessments for 16 commonly used tests, at six different time intervals between successive assessments, using five reliable change indices.

Methods

The study is part of the Normacog project, in which 388 healthy participants recruited in Spain (aged 18–84 years) were assessed on two occasions. A baseline assessment was carried out, and then followed up at 1 month (n = 67), 3 months (n = 64), 6 months (n = 59), 9 months (n = 60), 12 months (n = 68), or 24 months (n = 70). Longitudinal data were analyzed, and reliable change indices were calculated.

Results

A significant improvement was observed between assessment scores for all time points, especially in memory-related variables. Reference data are provided using the following indices: discrepancy scores expressed in percentiles, standard deviation index (SDI), reliable change index (RCI), RCI + practice effect (RCI + PE), and standardized regression-based formulae.

Conclusions

This study provides data to analyze whether or not a cognitive change can be considered reliable. The results support the use of these reliable change indices to avoid biases related to successive assessments. This study will lay the foundations for the implementation of these tools in clinical practice, and will be a reference for the creation of reliable change indices.