Speed and time, texts and sentences: Choosing the best metric for relating reading rate to comprehension

The objective of this study was to explore the relationship of reading rate to reading comprehension using different scales for reading rate. Although fluency research typically measures reading rate as speed (in words-per-minute) using whole texts as the text unit of interest, reading research investigating situation models measures rate as time (in seconds) using individual sentences as the unit of interest. The current study compared the predictive powers of these contrasting metrics. Time was shown to be the superior metric when both text- and sentence-reading times were included as predictors of comprehension, along with an interaction between them. The time model accounted for the curvilinear nature of the relationship and explained almost half of the variance in comprehension without violating the homoscedasticity assumption.