Editing Fitts's law (section)

== Bits per second: model innovations driven by information theory ==
The formulation of Fitts's index of difficulty most frequently used in the [[human–computer interaction]] community is called the Shannon formulation:

<math display="block">\text{ID} = \log_2 \Bigg(\frac{D}{W}+1\Bigg)</math>

This form was proposed by Scott MacKenzie,<ref>{{cite web|url=http://www.yorku.ca/mack|title=Scott MacKenzie's home page|first=I. Scott|last=MacKenzie|website=www.yorku.ca}}</ref> professor at [[York University]], and named for its resemblance to the [[Shannon–Hartley theorem]].<ref name=MacKenzie1992>{{cite journal	|last=MacKenzie	|first=I. Scott	|date=1992 |title=Fitts' law as a research and design tool in human–computer interaction |journal=Human–Computer Interaction |volume=7 |pages=91–139 |url=http://www.yorku.ca/mack/hci1992.pdf |doi=10.1207/s15327051hci0701_3|s2cid=14313454	}}</ref> It describes the transmission of information using bandwidth, signal strength and noise. In Fitts's law, the distance represents signal strength, while target width is noise.

Using this form of the model, the difficulty of a pointing task was equated to a quantity of information transmitted (in units of bits) by performing the task. This was justified by the assertion that pointing reduces to an information processing task. Although no formal mathematical connection was established between Fitts's law and the Shannon-Hartley theorem it was inspired by, the Shannon form of the law has been used extensively, likely due to the appeal of quantifying motor actions using information theory.<ref>{{Cite book |last=Drewes |first=Heiko |title=Extended Abstracts of the 2023 CHI Conference on Human Factors in Computing Systems |chapter=The Fitts' Law Filter Bubble |date=2023-04-19 |chapter-url=https://dl.acm.org/doi/10.1145/3544549.3582739 |language=en |publisher=ACM |pages=1–5 |doi=10.1145/3544549.3582739 |isbn=978-1-4503-9422-2|s2cid=258217343 }}</ref> In 2002 the [[ISO 9241]] was published, providing standards for human–computer interface testing, including the use of the Shannon form of Fitts's law. It has been shown that the information transmitted via serial keystrokes on a keyboard and the information implied by the ''ID'' for such a task are not consistent.<ref name=Soukoreff2011>{{cite journal |last1=Soukoreff |first1=R. William |last2=Zhao |first2=Jian |last3=Ren |first3=Xiangshi |title=The Entropy of a Rapid Aimed Movement: Fitts' Index of Difficulty versus Shannon's Entropy |year=2011 |journal=Human Computer Interaction |pages=222–239}}</ref> The Shannon-Entropy results in a different information value than Fitts's law. The authors note, though, that the error is negligible and only has to be accounted for in comparisons of devices with known entropy or measurements of human information processing capabilities.