Commentary on “A new indicator for the measurement of change with ordinal scores”

The paper by Ferreira et al. [1] introduces a new statistic—the Indicator of Positive Change (IpC)—that evaluates, at the group-level, improvement on an ordinal rating scale following some intervention. As the authors point out, it is not uncommon to see distributional assumptions from interval or ratio scales improperly applied to ordinal scale data. Misapplying these assumption leads to the use of inappropriate statistical procedures for analysis of ordinal scale data, which often results in inaccurate and unwarranted interpretations. The IpC is proposed as a new approach for calculating a standardized statistic that captures the magnitude of group-level improvement on an ordinal scale measure without reliance upon distributional assumptions, which would avoiding these common problems. …