Web Accessibility for Older Adults: Effects of Line Spacing and Text Justification on Reading Web Pages
Helen Petrie, Sorachai Kamollimsakul, Christopher Power · 2013 · Proceedings of the 15th International ACM SIGACCESS Conference on Computers and Accessibility (ASSETS) · doi:10.1145/2513383.2513414
Summary
This poster paper empirically tests two common web accessibility recommendations for older adults: increased line spacing and left-only text justification. The authors note that at least 10 sets of guidelines for making websites accessible to older people exist in English alone, yet few provide empirical evidence for their recommendations. Three guideline sets — AgeLight, SilverWeb, and NIA/NLM — all recommend increased line spacing and left justification, but with varying specificity. The study used a three-way mixed design with 24 participants: 12 older adults (ages 65-78, mean 72.8) and 12 younger adults (ages 24-31, mean 26.4). Each participant completed six information-finding tasks on a website about the Olympic Games, experiencing all six combinations of line spacing (single, 1.5, and double) and text justification (left-only and left-right). Performance was measured by task completion rate, time spent reading, number of pages visited, and subjective preference ratings on 5-point Likert scales.
Key findings
Neither line spacing nor text justification had a significant effect on any performance measure — task completion, reading time, and pages visited were statistically equivalent across all conditions for both age groups. However, preference data told a different story. Both younger and older adults significantly preferred 1.5 or double line spacing over single spacing, with no significant difference between 1.5 and double spacing. There was no significant preference difference between left-only and left-right justification for either age group. These findings challenge common guideline recommendations in two ways: first, increased line spacing should be recommended for all users, not just older adults, since younger participants showed the same preferences; second, no recommendation on text justification is needed, as neither age group showed a meaningful preference or performance difference between the two options.
Relevance
This study is a valuable example of empirically testing accessibility guidelines rather than accepting them as received wisdom. Many web accessibility recommendations, particularly those targeting older adults, are based on assumptions or expert opinion rather than user data. The finding that increased line spacing benefits all users equally — not just older adults — supports the broader principle that accessibility improvements often enhance the experience for everyone. For web developers, the practical takeaway is to use 1.5 or double line spacing as a default and not worry about text justification as an accessibility concern. The study is limited by its small sample size and the specific task type (information finding), but it contributes to the important project of building an evidence base for accessibility guidelines.
Tags: older adults · web accessibility · typography · line spacing · text justification · readability · web design guidelines · aging
Standards referenced: WCAG