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ABSTRACT
For decades, Fitts' law (1954) has been used to model pointing time in user interfaces. As with any rapid motor act, faster pointing movements result in increased errors. But although prior work has examined accuracy as the "spread of hits," no work has formulated a predictive model for error rates (0-100%) based on Fitts' law parameters. We show that Fitts' law mathematically implies a predictive error rate model, which we derive. We then describe an experiment in which target size, target distance, and movement time are manipulated. Our results show a strong model fit: a regression analysis of observed vs. predicted error rates yields a correlation of R2=.959 for N=90 points. Furthermore, we show that the effect on error rate of target size (W) is greater than that of target distance (A), indicating a departure from Fitts' law, which maintains that W and A contribute proportionally to index of difficulty (ID). Our error model can be used with Fitts' law to estimate and predict error rates along with speeds, providing a framework for unifying this dichotomy.
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INDEX TERMS
Primary Classification:
H.
Information Systems
H.5
INFORMATION INTERFACES AND PRESENTATION (I.7)
H.5.2
User Interfaces (D.2.2, H.1.2, I.3.6)
Subjects:
Theory and methods
Additional Classification:
H.
Information Systems
H.1
MODELS AND PRINCIPLES
H.1.2
User/Machine Systems
Subjects:
Human factors
General Terms:
Experimentation,
Human Factors,
Theory
Keywords:
clicking errors,
error model,
error rates,
fitts' law,
mousing errors,
movement time,
pointing errors,
pointing time,
schmidt's law,
speed-accuracy tradeoff
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