Measuring Keyboard Performance for People with Disabilities
Edmund LoPresti, Heidi Horstmann Koester, Richard C. Simpson · 2006
Fourteen individuals with various motor impairments performed a series of text entry exercises. Performance measures were collected which indicate overall performance (speed and error rate) and classification of errors. Such performance metrics could be useful in assessing the computer access skills of clients, and recommending software, hardware, or training interventions. BACKGROUND People with disabilities may have difficulty performing text entry tasks using a computer keyboard. The specific types of difficulty will vary depending on the person’s intrinsic abilities, the input device being used, and the task. In order to understand and remediate the difficulties faced by a particular individual, it is desirable to quantify performance and classify errors. This aids in comparing performance over time or between input devices; evaluating the success of an intervention; or communicating the client’s need for an intervention. General measures of typing performance include text entry rate and accuracy. A typical measure of text entry rate is the number of words per minute. It is more difficult to measure error rate in a consistent manner, given the variety of ways in which someone can make an error. Soukoreff and MacKenzie have proposed a measure of error rate using the mean string distance (MSD) (1). The MSD between two strings of characters is the minimum number of primitives – character insertions, deletions, or substitutions – necessary to transform one string into the other. This provides a measure of the difference between a string of characters entered by the user and the correct string.