%0 Journal Article
%T A Note on the Validity of the Shannon Formulation for Fitts¡¯ Index of Difficulty
%A Ian Scott MacKenzie
%J Open Journal of Applied Sciences
%P 360-368
%@ 2165-3925
%D 2013
%I Scientific Research Publishing
%R 10.4236/ojapps.2013.36046
%X <p>
	<span>The three most common variations of Fitts¡¯
index of difficulty are the Fitts formulation, the Welford formulation, and the
Shannon formulation.</span><span> </span><span>A recent paper by Hoffman</span><span>n</span><span> [1]</span><span> </span><span>critiqued the three and concluded that
the Fitts and Welford formulations are valid and that the Shannon formulation is
invalid. In this paper,</span><span> </span><span>we challenge Hoffmann¡¯s position regarding the Shannon
formulation.</span><span> </span><span>It is argued that
the issue of validity vs. invalidity is ill-conceived, given that Fitts¡¯ law is
a ¡°model by analogy¡± with no basis in human motor control. The relevant questions
are of utility: Does a model work? How well? Is it useful? Where alternative formulations
exist, they may be critiqued and compared for strengths and weaknesses, but validity
is an irrelevant construct. In a reanalysis of data from Fitts¡¯ law experiments,
models built using the Shannon formulation are (re)affirmed to be as good as, and
generally better than, those built using the Fitts or Welford formulation.</span><span></span> 
</p>
%K Fitts¡¯ Law
%K Index of Difficulty
%K Shannon Formulation
%K Effective Target Width
%K Scientific Method
%U http://www.scirp.org/journal/PaperInformation.aspx?PaperID=38031