GOMS

toc

=GOMS=

//GOMS// is a model for describing human task performance, and was proposed by Card, Moran, and Newell in 1983 (Usability First 2006). In terms of analysis methods, it is considered to be the most famous and long-lasting of a large number of cognitive tasks. GOMS is an acronym for **G**oals, **O**perators, **M**ethods and **S**election Rules (Benyon 2005). According to a research of Kieras, the GOMS model is very useful in obtaining meaningful and accurate predictions of learning and time execution (Kieras Research).

The GOMS model is generally composed of four main parts, which are: > > >
 * **Goals** - are the tasks that the user is trying to accomplish by use of a system. For instance, turning on the television to watch television shows
 * **Operators** - refers to tasks that are needed to accomplish //goals//. These are the actions that are required in order to make the system work. For instance, in watching television people must press the power button, and press the channel buttons in order to switch between channels.
 * **Methods** - represent the steps of operators grouped together, to accomplish a single goal. These methods can either be sub-tasks and operators. Things such as entering the channel would be considered as subtasks.
 * **Selection rules** - These are the decisions that have to be taken in order to choose a //method// from among alternate methods to finally accomplish the goal. For instance, in watching television, one can use the remote, or the television itself to control the television (i.e. scrolling through channels, turning on the television, adjusting volume, etc...)

There are many different types of GOMS, such as the CMN-GOMS Variation, KLM-GOMS Variation, and NGOMSL Variation (Wikipedia 2006). However, the GOMS model is only useful if the people know what they are going to do. For instance, Selection rules must be well learned in order for it to be successful. GOMS is not a method where people are problem solving, instead, it is used by designers to help them think about different designs for their product. Furthermore,similiar to the HTA (Hierarchical Task Analysis) GOMS need to describe, organize and structure the tasks in a hierarchical way (Benyon 2005).

Weaknesses and Limitations
Although the GOMS analysis provides almost an accurate measurement of analysis, it also possesses certain limitations and weaknesses. Even though the GOMS model provides useful and accurate estimation of its activities, it does not take into considerations the user's fatigue. If the user is easily fatigued, it may take him/her longer to complete a certain task, making the overall GOMS model inaccurate. Fatigue applies not only physically but mentally also. The user may feel uninterested of the tasks assigned, because he/she is repeating similar tasks numerous times. In addition, the GOMS analysis only applies to expert users and not to beginners. The user must be fully aware of the tasks at hand, and if he/she is not aware, the analysis will be unsuccessful. In terms of users, the user's personality and work habits are also not considered in the GOMS model. Because the personalities and work habits are not considered in the GOMS model, it would prove to be difficult to estimate the amount of time needed to complete a task (Wikipedia).

=Relevant Examples=

An example of GOMS using the Heirarchical Task Analysis (HTA) (Benyon, 2005)is as follows:


 * Goal:** to send an email
 * Operator:** clicking the mouse over icons or scrolling through a taskbar to open email interface
 * Methods:** selecting a method through an address book or typing in the email manually
 * Selection rules:** selecting the contact's name through the email address book or type the first letter of the contact's name or type in nickname to automatically attach the email address to the nickname.

=Credits=

Benyon, David and Phil Turner, and Susan Turner. __"Designing Interactive Systems (People, Activities, Contexts, Technologies)".__ 2005. Spain. Pearson Education Limited. GOMS Models: An Approach to Rapid Usability Evaluation. http://www.eecs.umich.edu/~kieras/goms.html Other types of GOMS and weaknesses and limitations - http://en.wikipedia.org/wiki/GOMS Usability First. Information about GOMS. 2006. http://www.usabilityfirst.com/methods/goms.txl

[|Back to Top]