## Abstract

For evaluating the performance of color-difference equations, several goodness-of-fit measures were proposed in the past, such as Pearson’s correlation coefficient (*r*), the performance factor $PF/3$, and the recently proposed standardized residual sum of squares (*STRESS*) measure. The *STRESS* shares its main advantage, which is the possibility to statistically test performance differences, with the correlation coefficient. We show, by mathematical analysis supported by instructive numerical examples, that the *STRESS* has no meaningful interpretation in this regression analysis context. In addition, we present objections to the use of the *STRESS* for evaluating color- difference equations. Therefore, we recommend using the correlation coefficient in combination with a graphical and diagnostics analysis to ensure proper application as with any statistical technique.

© 2011 Optical Society of America

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