GOMS at a Glance...

CS 5724: Models and Theories of Human-Computer Interaction
Fall 1996
House of GOMS

Precis

GOMS is an acronym that stands for GOALS, OPERATORS, METHODS, and SELECTION RULES. A GOMS model is composed of METHODS that are used to achieve specific GOALS. The METHODS are then composed of OPERATORS at the lowest level. The OPERATORS are specific steps that a user performs and are assigned a specific execution time. If a GOAL can be achieved by more than one METHOD, then SELECTION RULES are used to determine the proper METHOD.

Scientific Foundation

Since 1983, with the publication of the Card, Moran, and Newell book, GOMS has provided a framework for analyzing routine human computer interactions. GOMS has it's scientific foundation in cognitive psychology and is an improvement on earlier human factors modeling.

Methods and Information

There are basically four different GOMS models. The four models are the Keystroke-Level Model (KLM), CMN-GOMS, NGOMSL, and CPM-GOMS. These four models vary in complexity and are used to model different activities. There are different ways to construct GOMS models depending on which flavor of GOMS that is applied. For an example of constructing a GOMS model using the CMN-GOMS method see the Goms Watch Analysis.

Results

GOMS can be used both both quantitatively and qualitatively. Quantitatively, it gives good predictions of performance time and learning. If, for instance, you have to choose between two systems, say you must decide whether your company should buy this or that package of office automation tools, you can apply a GOMS model. To do this, build a GOMS model of Application A and a GOMS model of Application B, and examine the quantitative predictions. Perhaps Application A has a lower up-front capital cost, but will be slower to perform frequent tasks. Perhaps Application B will be faster to perform tasks, but has a longer learning time. With these quantitative predictions, you can examine such tradeoffs in the light of what is important to your company, and what is relevant to your user-group or task situation. This is exactly how NYNEX arrived at a choice of telephone-operator workstations. Qualitatively, GOMS can be used to design training programs and help systems. The GOMS model is a careful description of the knowledge needed to perform a given task and thus it describes the content of task-oriented documentation. You only need to tell the new user what the goals are, what different methods could be used to achieve them, and when to use each method(selection rules). This approach has been shown to be an efficient way to organize help systems, tutorials, and training programs as well as user documentation.

Applications

GOMS can be used in various application and fields. Some GOMS application examples include but are not limited to: All of these application topics can be found in Kieras and John, 1994.

Limitations

Card et al. (1980) provided the most detailed list of the weaknesses of GOMS. The weaknesses are as follows: