Perceptual Biases in Font Size as a Data Encoding

TLDR

Many visualizations, including word clouds, cartographic labels, and word trees, encode data within the sizes of fonts, but font size can bias perception by conflating word length, letter count, or character height. The study highlights the largest potential biases in font‑size encoding. It describes a strategy to mitigate these biases. Empirical studies show that irrelevant factors influence comparative judgments of font size, though less than conventional wisdom might suggest.

Abstract

Many visualizations, including word clouds, cartographic labels, and word trees, encode data within the sizes of fonts. While font size can be an intuitive dimension for the viewer, using it as an encoding can introduce factors that may bias the perception of the underlying values. Viewers might conflate the size of a word's font with a word's length, the number of letters it contains, or with the larger or smaller heights of particular characters ('o' versus 'p' versus 'b'). We present a collection of empirical studies showing that such factors-which are irrelevant to the encoded values-can indeed influence comparative judgements of font size, though less than conventional wisdom might suggest. We highlight the largest potential biases, and describe a strategy to mitigate them.