Logistic versus linear regression-based Reliable Change Index: implications for clinical studies with diverse sample sizes
The linear regression-based Reliable Change Index (RCI) is widely used to identify memory impairments through longitudinal assessment. However, the minimum sample size required for estimates to be reliable has never been specified. Using the Alzheimer’s Disease Neuroimaging Initiative data as true parameters, we run simulations for samples of size 10 to 1000 and analyzed the percentage of times the estimates are significant, their coverage rate, and the accuracy of the models including both the True Positive Rate (TPR) and the True Negative Rate (TNR). We compared the linear RCI with a logistic RCI for discrete, bounded scores. We found that the logistic RCI is more accurate than the linear RCI overall, with the linear RCI approximating the logistic RCI for samples of size 200 or greater. We provide an R code for researchers and clinicians to calculate the logistic RCI with samples smaller than 200.