We studied the extent to which time-on-task is correlated with perception of usability for people who are familiar with a phone model and for those who are not. Our controlled experiment, conducted in Japan, correlated subjective usability assessments with time-on-task for expert and novice users on three different mobile phone models. We found that the correlation between perceived usability and time-on-task is stronger when participants are more familiar with the phone model. While not significant when initially inspecting a new phone model, a negative correlation between time-on-task and perceived usability becomes significant with as little as an hours time doing tasks on the unfamiliar phone. This suggests that designing the UI to make time-on-task as short as possible may not have much effect on the purchase decision, but as experience increases, it may increase the loyalty of existing users.
Suzuki, S.; Bellotti, V.; Yee, N.; John, B. E.; Nakao, Y.; Asahi, T.; Fukuzumi, S. Variation in importance of time-on-task with familiarity with mobile phone models. ACM Conference on Human Factors in Computing Systems (CHI 2011); 2011 May 7-12; Vancouver, BC, Canada.