Fitts’ Law: On Calculating Throughput and Non-ISO Tasks
Abstract
We used a target-selection task to evaluate head-tracking as an input method for mobile devices. First, the method of calculating Fitts’ throughput is described by means of a raw data detailed example. Then, the method of calculating throughput is discussed for non-ISO tasks, since the procedure targets were randomly positioned from trial to trial. Due to a non-constant amplitude within each sequence of trials, throughput was calculated using two methods of data aggregation: the first one, by sequence of trials using the mean amplitude, and the second one, by common A-W conditions. For each data set, we used four methods for calculating throughput. The grand mean for throughput (calculated through the division of means and the adjustment for accuracy) was of 0.74 bps, which is 45 % lower than the value obtained using an ISO task. We recommend to calculate throughput using the division of means plus the adjustment for accuracy, and to avoid using the reciprocal slope of the regression model. We present various design recommendations for non-ISO tasks, such as: i) to keep amplitude and constant target within each sequence of trials, and ii) to use strategies to avoid or remove reaction time.
References
[2] I. S. MacKenzie, “Fitts’ law as a research and design tool in human-computer interaction,” Human-Computer Interact., vol. 7, no. 1, pp. 91–139, 1992.
[3] R. W. Soukoreff and I. S. MacKenzie, “Towards a standard for pointing device evaluation, perspectives on 27 years of Fitts’ law research in HCI,” Int. J. Hum. Comput. Stud., vol. 61, no. 6, pp. 751–789, Dec. 2004.
[4] ISO, “9241--9. 2000. Ergonomics requirements for office work with visual display terminals (VDTs) -- Part 9: Requirements for non-keyboard input devices,” Int. Organ. Stand., 2002.
[5] ISO, “9241--411. 2012. Ergonomics of human-system interaction -- Part 411: Evaluation methods for the design of physical input devices,” Int. Organ. Stand., 2012.
[6] I. S. MacKenzie, “Fitts’ throughput and the remarkable case of touch-based target selection,” in Proceedings of the 17th International Conference on Human-Computer Interaction - HCII 2015, 2015, pp. 238–249.
[7] K. B. Perry and J. P. Hourcade, “Evaluating one handed thumb tapping on mobile touchscreen devices,” in Proceedings of the Graphics Interface 2008 - GI 2008, 2008, pp. 57–64.
[8] N. Henze and S. Boll, “It does not Fitts my data! Analysing large amounts of mobile touch data,” in Proceedings of the IFIP Conference on Human-Computer Interaction - INTERACT 2011, 2011, pp. 564–567.
[9] M. F. Roig-Maimó, J. Varona Gómez, and C. Manresa-Yee, “Face Me! Head-Tracker Interface Evaluation on Mobile Devices,” in Proceedings of the 33rd Annual ACM Conference Extended Abstracts on Human Factors in Computing Systems, 2015, pp. 1573–1578.
[10] Apple Inc, “iOS Human Interface Guidelines: Designing for iOS.” .
[11] P. M. Fitts and J. R. Peterson, “Information capacity of discrete motor responses.”
[12] R. W. Bailey, Human performance engineering: Designing high quality professional user interfaces for computer products, applications and systems, 3rd ed. Upper Saddle River, NJ: Prentice Hall, 1996.
[13] M. F. Roig-Maimó, I. S. MacKenzie, C. Manresa-Yee, and J. Varona, “Head-tracking interfaces on mobile devices: Evaluation using Fitts’ law and a new multi-directional corner task for small displays,” Int. J. Hum. Comput. Stud.
Downloads
