An Improved Rank Correlation Effect Size Statistic for Single-Case Designs: Baseline Corrected Tau. (July 2017)

• Record Type: Journal Article
• Authors: Tarlow, Kevin R.
• Is Part Of: Behavior modification. Volume 41:Number 4(2017:Jul.)
• Page Start: 427
• Page End: 467
• Publication Date: 2017-07
• Subjects: clinical outcomes assessment -- effect size -- measurement -- single case -- treatment effectiveness; Behavior modification -- Periodicals; Behavior therapy -- Periodicals; 153.85
• DOI: 10.1177/0145445516676750
• Languages: English
• ISSNs: 0145-4455

Abstract

Measuring treatment effects when an individual's pretreatment performance is improving poses a challenge for single-case experimental designs. It may be difficult to determine whether improvement is due to the treatment or due to the preexisting baseline trend. Tau- U is a popular single-case effect size statistic that purports to control for baseline trend. However, despite its strengths, Tau- U has substantial limitations: Its values are inflated and not bound between −1 and +1, it cannot be visually graphed, and its relatively weak method of trend control leads to unacceptable levels of Type I error wherein ineffective treatments appear effective. An improved effect size statistic based on rank correlation and robust regression, Baseline Corrected Tau, is proposed and field-tested with both published and simulated single-case time series. A web-based calculator for Baseline Corrected Tau is also introduced for use by single-case investigators.