Predicting text entry speed on mobile phones

We present a model for predicting expert text entry rates for several input methods on a 12-key mobile phone keypad. The model includes a movement component based on Fitts' law and a linguistic component based on digraph, or letter-pair, probabilities. Predictions are provided for one-handed thumb and two-handed index finger input. For the traditional multi-press method or the lesser-used two-key method, predicted expert rates vary from about 21 to 27 words per minute (wpm). The relatively new T9 method works with a disambiguating algorithm and inputs each character with a single key press. Predicted expert rates vary from 41 wpm for one-handed thumb input to 46 wpm for two-handed index finger input. These figures are degraded somewhat depending on the user's strategy in coping with less-than-perfect disambiguation. Analyses of these strategies are presented.

[1]  Colin G. Drury,et al.  A model for movement time on data-entry keyboards , 1992 .

[2]  Alex Chaparro,et al.  A Psychophysical Comparison of Two Stylus-Driven Soft Keyboards , 1999, Graphics Interface.

[3]  Abigail Sellen,et al.  A comparison of input devices in element pointing and dragging tasks , 1991, CHI.

[4]  I. Scott MacKenzie,et al.  Theoretical upper and lower bounds on typing speed using a stylus and a soft keyboard , 1995, Behav. Inf. Technol..

[5]  I.,et al.  Fitts' Law as a Research and Design Tool in Human-Computer Interaction , 1992, Hum. Comput. Interact..

[6]  S. Mackenzie,et al.  A comparison of input device in elemental pointing and dragging task , 1991, CHI 1991.

[7]  I. Scott MacKenzie,et al.  The design and evaluation of a high-performance soft keyboard , 1999, CHI '99.

[8]  Brian W. Epps.  Comparison of Six Cursor Control Devices Based on Fitts' Law Models , 1986 .

[9]  E. Hoffmann,et al.  Geometrical conditions for ballistic and visually controlled movements. , 1988, Ergonomics.

[10]  Gale L. Martin.  Configuring a numeric keypad for a touch screen , 1988 .

[11]  I. Scott MacKenzie,et al.  A Probabilistic Character Layout Strategy for Mobile Text Entry , 1998, Graphics Interface.

[12]  I. Scott MacKenzie,et al.  Extending Fitts' law to two-dimensional tasks , 1992, CHI.

[13]  P. Fitts.  The information capacity of the human motor system in controlling the amplitude of movement. , 1954, Journal of experimental psychology.

[14]  Allen Newell,et al.  The psychology of human-computer interaction , 1983 .