About universal solutions for designing interfaces that don’t exist. Fitts’s and Hick’s laws.
What is better? Interface solution A or interface solution B? Using dialog boxes, or better to avoid using of them? Locate main menu at the left top or at any other place of the page?
There are many questions that are very difficult to give definite and clear answers, because something tells (experience?) that: universal solutions, which are working always, almost none. But there are general laws that are always working productive. Unfortunately, discovered and proved only a small part of them – actually, only Fitts’s and Hick’s laws.
Fitts’s law has been formulated mathematically in several different ways. One common form is the Shannon formulation (proposed by Scott MacKenzie, professor of York University, and named for its resemblance to the Shannon-Hartley theorem) for movement along a single dimension:
where: T is the average time taken to complete the movement. (Traditionally, researchers have used the symbol MT for this, to mean movement time.)a represents the start/stop time of the device and b stands for the inherent speed of the device. These constants can be determined experimentally by fitting a straight line to measured data.D is the distance from the starting point to the center of the target. (Traditionally, researchers have used the symbol A for this, to mean the amplitude of the movement.)W is the width of the target measured along the axis of motion. W can also be thought of as the allowed error tolerance in the final position, since the final point of the motion must fall within ±W⁄2 of the target’s center. From the equation, we see a speed-accuracy trade off associated with pointing, whereby targets that are smaller and/or further away require more time to acquire.Hick’s Law, named after British psychologist William Edmund Hick, or the Hick–Hyman Law (for Ray Hyman), describes the time it takes for a person to make a decision as a result of the possible choices he or she has. The Hick-Hyman Law assesses cognitive information capacity in choice reaction experiments. The amount of time taken to process a certain amount of bits in the Hick-Hyman Law is known as the rate of gain of information. Given n equally probable choices, the average reaction time T required to choose among them is approximately T = blog2(n + 1) where b is a constant that can be determined empirically by fitting a line to measured data. Operation of logarithm here expresses depth of “choice tree” hierarchy. Basically log2 means that you perform binary search. According to Card, Moran, and Newell (1983), the +1 is “because there is uncertainty about whether to respond or not, as well as about which response to make.”
Hick’s Law is similar in form to Fitts’s law. Intuitively, one can reason that Hick’s Law has a logarithmic form because people subdivide the total collection of choices into categories, eliminating about half of the remaining choices at each step, rather than considering each and every choice one-by-one, requiring linear time. Hick’s Law is sometimes cited to justify menu design decisions. However, applying the model to menus must be done with care. For example, to find a given word (e.g. the name of a command) in a randomly ordered word list (e.g. a menu), scanning of each word in the list is required, consuming linear time, so Hick’s law does not apply. However, if the list is alphabetical and the user knows the name of the command, he or she may be able to use a subdividing strategy that works in logarithmic time.
Interesting that all these laws do not say anything about the specific interface – they describe the person and especially his perception / behavior, and not the interfaces. I think that it will be continued, that never and no one can come up with ‘General Universal Theory about Interfaces’. Hence, there can be no faith in the possibility of common answers to common questions about the interface.
To prove the efficiency of interface solutions can only testing. The abundance of factors affecting the efficiency of front-end solutions not allows to limit the search of general answers using simple reasoning – the reasoning will be very long and hard. But if the reasoning is long, then the probability of error increases. Why search for answers, knowing that they could be wrong? But if you’re interested in a specific question about a specific interface – everything is just easy. Test it. If testing shows that the interface works, then it really works))