Theoretical upper and lower bounds on typing speed using a stylus and a soft keyboard

TLDR

The model builds on Hick–Hyman choice reaction time, Fitts law for aimed movements, and English digram frequency tables to characterize text‑entry tasks on soft keyboards. The study presents a theoretical model to predict the upper and lower bounds of typing speed with a stylus on a soft QWERTY keyboard. The model incorporates the Hick–Hyman law, Fitts law, and a 27×27 digram table that includes the space character and position‑specific digram probabilities, and compares its predictions with empirical stylus‑based text‑entry studies. It predicts novice users can type at 8.9 wpm and experts at 30.1 wpm.

Abstract

Abstract A theoretical model is presented to predict upper-and lower-bound text-entry rates using a stylus to tap on a soft QWERTY keyboard. The model is based on the Hick-Hyman law for choice reaction time, Fitts law for rapid aimed movements, and linguistic tables for the relative frequencies of letter-pairs, or digrams, in common English. The model's importance lies not only in the predictions provided, but in its characterization of text-entry tasks using keyboards. Whereas previous studies only use frequency probabilities of the 26 × 26 digrams in the Roman alphabet, our model accommodates the space har—the most common character in typing tasks. Using a very large linguistic table that decomposes digrams by position-within-words, we established start-of-word (space-letter) and end-of-word (letter-space) probabilities and worked from a 27 × 27 digram table. The model predicts a typing rate of 8.9wpm for novices unfamiliar with the QWERTY keyboard, and 30.1wpm for experts. Comparisons are drawn with empirical studies using a stylus and other forms of text entry.