One of the most basic rules in interface design is known as Fitts’ Law , after Paul Fitts, a psychologist at Ohio State University who studied human response time in rapid aimed movements. Basically, Fitts’ model claimed that accuracy in rapid hand movements decreases in inverse relation to the distance from and size of the target. GUIs hadn’t even been conceived of at that time, yet his model has had an immense effect on the design of the computer programs and websites we use today.
However, Fitts’ original experiment and predictions based on the experiment all refer to a 1-dimensional target (a particular point on a screen, for example), rather than a 2-dimensional target like a word or a box or a menu item. A group at UC Berkeley have developed a web-based experiment designed to test Fitts’ Law as well as an alternative model they have proposed. Take a couple of minutes to try it out and help them gather data points for their study.