WASET
	%0 Journal Article
	%A Hidehiko Okada and  Takayuki Akiba
	%D 2014
	%J International Journal of Computer and Information Engineering
	%B World Academy of Science, Engineering and Technology
	%I Open Science Index 85, 2014
	%T Evaluation of Fitts’ Law Index of Difficulty Formulation for Screen Size Variations
	%U https://publications.waset.org/pdf/9997694
	%V 85
	%X It is well-known as Fitts’ law that the time for a user to point a target on a GUI screen can be modeled as a linear function of “index of difficulty (ID).” In this paper, the authors investigate whether the traditional ID formulation is appropriate independently of device screen sizes. Result of our experiment reveals that the ID formulation may not consistently capture actual difficulty: users’ pointing performances are not consistent among pointing target variations of which index of difficulty are consistent. The term A/W may not be appropriate because the term causes the observed inconsistency. Based on this finding, the authors then evaluate the applicability of possible models other than Fitts’ one. Multiple regression models are found to be able to appropriately represent the effects of target design variations. The authors next make an attempt to improve the definition of ID in Fitts’ model. Our idea is to raise the size or the distance values depending on the screen size. The modified model is found to fit well to the users’ pointing data, which supports the idea. 

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