Ben Sawyer^1,2, Md Manumur Rashid^1,2, Hilary Palmen³, Mert Kucuk¹, Nilsu Atilgen¹; ¹The Readability Consotium, ²The University of Central Florida, ³Google Fonts

The relationship between print size and reading speed is well-established, with larger sizes resulting in larger image on the retina. This benefits populations such as older adults and individuals with visual impairments (Legge et al., 1985). However, in reading research, "size" is sometimes discussed in terms of x-height, which refers to the height of lowercase letters in a font. Importantly, x-height and print size are distinct; different fonts can have varying x-heights even at the same nominal size, potentially influencing readability. To investigate this distinction, we examined the combined effects of print size and x-height on reading speed. Participants (N = 60) read passages at varying sizes and x-heights, followed by comprehension questions. A repeated-measures ANOVA revealed that, as expected, print size significantly impacted reading speed (p < .05), while x-height alone did not (p = .134). To explore the relationship further and account for individual variability, we conducted a linear mixed-effects model analysis. This deeper analysis revealed an interaction between size and x-height. Specifically, when print size was small, participants read marginally faster with larger x-heights (mean = 248 WPM) compared to smaller x-heights (mean = 232 WPM). This effect was not observed at larger print sizes. These findings confirm that print size is a critical factor in reading speed across all conditions. Additionally, x-height plays a role in enhancing readability when print size is small and reading becomes more challenging. This insight is particularly relevant in scenarios where increasing print size is not feasible; selecting fonts with larger x-heights may offer an alternative strategy to improve readability.

Acknowledgements: The Readability Consortium