Duration-adjusted Reliable Change Index (DaRCI): Defining clinically relevant symptom changes of varying durations

Identifying relevant symptom shifts as they enfold can be challenging, as the time period over which they take place is not uniform for all people. This paper proposes an adaptation of the well-established Reliable Change Index (RCI) that allows researchers and clinicians to explore the presence of symptom changes of varying durations in individual patients’ time series: the Duration-adjusted RCI (DaRCI). The DaRCI takes the RCI cut-off score for change between two points as a starting point, and proportionally extends this measure over multiple observations, while maintaining reliability at a given confidence level. Researchers must choose the relevant time period between two observations, and additional increments are added accordingly.
To illustrate the ability of this method to detect changes of various durations, simulated depressive symptom time series with varying degrees of discontinuity and overall mean change in scores were used. The results show that the DaRCI thresholds over two, three and four observations were effective at identifying the simulated change periods over multiple time points, starting from relatively gradual change slopes (picking up reliable changes in 20-60% of simulated time series if the overall change was large enough), to highly discontinuous changes (up to 100% accuracy).
The DaRCI may be particularly useful for identifying shifts in symptoms that appear relatively abrupt, which can help indicate when a patient is showing significant improvement or deterioration. Its ease of use makes it suitable for application in the clinical context, and is a promising method to explore different change durations in clinical populations.