Selecting an appropriate scan rate: the ".65 rule".
Investigators have discovered that the ratio between a user's reaction time and an appropriate scan rate for that user is approximately .65, which we refer to as "the .65 rule." As part of a larger effort to develop software that automatically adapts the configuration of switch access software, data were collected comparing subject performance with a scan rate chosen using the .65 rule and a scan rate chosen by the user. Analysis of the data indicates that for many people, the .65 rule produces a scan rate that is approximately the same as the average switch press time plus 2 standard deviations. Further analysis demonstrates a relationship between the coefficient of variation (the standard deviation divided by the mean) and error rate. If accurate information is available about the mean, standard deviation, and distribution of a client's switch press time, a scan rate can be chosen that will yield a specific error level. If a rigorous statistical approach is impractical, the .65 rule will generally yield a usable scan rate based on mean press time alone.
Simpson
Richard
R
Department of Rehabilitation Science & Technology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA. ris20@pitt.edu
Koester
Heidi
H
LoPresti
Ed
E
D000328:Adult; D006233:Persons with Disabilities; D004496:Education, Continuing; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010414:Pennsylvania; D012656:Self-Help Devices; D013647:Task Performance and Analysis; D014584:User-Computer Interface