The time it takes to make a decision increases as the number of alternatives increases.1
Hick’s Law states that the time required to make a decision is a function of the number of available options. It is used to estimate how long it will take for people to make a decision when presented with multiple choices. For example, when a pilot has to press a particular button in response to some event, such as an alarm, Hick’s Law predicts that the greater the number of alternative buttons, the longer it will take to make the decision and select the correct one. Hick’s Law has implications for the design of any system or process that requires simple decisions to be made based on multiple options.2
All tasks consist of four basic steps: (1) identify a problem or goal, (2) assess the available options to solve the problem or achieve the goal, (3) decide on an option, and (4) implement the option. Hick’s Law applies to the third step: decide on an option. However, the law does not apply to decisions that involve significant levels of searching, reading, or complex problem solving. For example, a complex task requiring reading sentences and intense concentration with three options can easily take longer than a simple stimulus-response task with six options. Therefore, Hick’s Law is most applicable for simple decision-making tasks in which there is a unique response to each stimulus. For example, if A happens, then push button 1, If B happens, then push button 2. The law is decreasingly applicable as the complexity of tasks increases.3
Designers can improve the efficiency of a design by understanding the implications of Hick’s Law. For example, the law applies to the design of software menus, control displays, wayfinding layout and signage, and emergency response training—as long as the decisions involved are simple. As the complexity of the tasks increases, the applicability of Hick’s Law decreases. For example, Hick’s Law does not apply to complex menus or hierarchies of options. Menu selection of this type is not a simple decision-making task since it typically involves reading sentences, searching and scanning for options, and some level of problem solving.
Consider Hick’s Law when designing systems that involve decisions based on a set of options. When designing for time-critical tasks, minimize the number of options involved in a decision to reduce response times and minimize errors. When designs require complex interactions, do not rely on Hick’s Law to make design decisions; rather, test designs on the target population using realistic scenarios.
In training people to perform time-critical procedures, train the fewest possible responses for a given scenario. This will minimize response times, error rates, and training costs.
See also Errors, Fitts’ Law, Progressive Disclosure, and Wayfinding.