<P> Accurate assumptions are vital in GOMS analysis . Before applying the average times for detailed functions, it is very important that an experimenter make sure he or she has accounted for as many variables as possible by using assumptions . Experimenters should design their GOMS analysis for the users who will most likely be using the system which is being analyzed . Consider, for example, an experimenter wishes to determine how long it will take an F22 Raptor pilot to interact with an interface he or she has used for years . It can probably be assumed that the pilot has outstanding vision and is in good physical health . In addition, it can be assumed that the pilot can interact with the interface quickly because of the vast hours of simulation and previous use he or she has endured . All things considered, it is fair to use fastman times in this situation . Contrarily, consider an 80 - year - old person with no flight experience attempting to interact with the same F22 Raptor interface . It is fair to say that the two people would have much different skill sets and those skill sets should be accounted for subjectively . </P> <P> The only way to account for errors in GOMS analysis is to predict where the errors are most likely to occur and measure the time it would take to correct the predicted errors . For example, assume an experimenter thought that in typing the word "the" it was likely that a subject would instead incorrectly type "teh ." The experimenter would calculate the time it takes to type the incorrect word, the time it takes to recognize that a mistake has been made, and the time it takes to correct the recognized error . </P> <P> A successful implementation of CPM - GOMS was in Project Ernestine held by New England Telephone . New ergonomically designed workstations were compared to old workstations in terms of improvement in telephone operators' performance . CPM - GOMS analysis estimated a 3% decrease in productivity . Over the four - month trial 78,240 calls were analysed and it was concluded that the new workstations produced an actual 4% decrease in productivity . As the proposed workstation required less keystrokes than the original it was not clear from the time trials why the decrease occurred . However CPM - GOMS analysis made it apparent that the problem was that the new workstations did not utilize the workers' slack time . Not only did CPM - GOMS give a close estimate, but it provided more information of the situation . </P> <P> GOMS models were employed in the redesign of a CAD (computer - aided design) system for industrial ergonomics . An applied GOMS model shows where the interface needs to be redesigned, as well as provides an evaluation of design concepts and ideas . In Richard Gong's example, when GOMS revealed a frequent goal supported by a very inefficient method, he changed the method to a more efficient one . If GOMS showed that there were goals not supported by any method at all, then new methods were added . GOMS also revealed where similar goals are supported by inconsistent methods, a situation in which users are likely to have problems remembering what to do, and showed how to make the methods consistent . </P>

Using goms for user interface design and evaluation which technique