GOMS

GOMS is a family of predictive models of human performance that can be used to improve the efficiency of human-machine interaction by identifying and eliminating unnecessary user actions. GOMS stands for (Goals, Operators, Methods, and Selection).

The simplest and most frequently used GOMS variant is KLM-GOMS (Keystroke-Level Model), where empirically derived values for basic operators like keystrokes, button presses, double clicks, and pointer movement time, are used to estimate task times.

The other three major GOMS variants (CMN-GOMS, NGOMSL, and CPM-GOMS) require extensive training and familiarity with Human-Computer Interaction principles to perform an analysis.

Related Links

Baumeister, L.K., John, B.E., & Byrne, M.D. (2000). A comparison of tools for building GOMS Models Tools for Design. In Proc. of ACM Conf. on Human Factors in Computing Systems CHI’2000 (The Hague, 1-6 April 2000). ACM Press, New York. 502–509.

Gray, W. D., & John, B. E. (1993). Project Ernestine: Validating a GOMS Analysis for Predicting and Explaining Real-World Task Performance.

John, B. E., & Kieras, D. E. (1996). Using GOMS for User Interface Design and Evaluation: Which Technique? This article describes the different GOMS techniques and when they should be used.

Kieras, D. E. (2006) A Guide to GOMS Model Usability Evaluation using GOMSL and GLEAN4 This document is a heavily modified version of the earlier “Guides” to GOMS modeling, Kieras (1988, 1997a), and supersedes the 1999 Guide referring to GLEAN3. It contains detailed information about GOMS, its strengths and limitations, how to construct a GOMS model with examples, and how to use a GOMS model to predict human performance.

Detailed Description

GOMS is a cognitive model of human-computer interaction that helps to better understand a task flow by decomposing it into atomic pieces. Once a flow has been decomposed, the sequence can be drawn visually and parallel and serial interactions shown graphically. This helps the analyst to eliminate unnecessary dependencies in the flow, or redesign the flow so that it contains fewer interactions along the critical path. A critical path is shortest path available that contains only interactions that are critical to execute the task all the way to goal completion.

Definitions for these terms are listed below.

• A Goal is defined as the successful end state for the task. For example, “Update my mailing address.”

• An Operator is an action performed on the machine. On a computer, this essentially breaks down into keystrokes and mouse clicks needed to achieve the goal of “Update my mailing address.”

• A Method is a series of Operators chained together to form a single unit. A single method might be “Click on the OK button,” which contains the Operators (move the hand to the mouse, point the mouse to the OK button, click the mouse, release the mouse , move the hand back to keyboard)

• A Selection is a decision made, and this is required when a task flow has parallel actions. For example, the user might “Click on the OK button” using the chain of Operators above, or might simply press the ENTER key. The ENTER key is obviously much more efficient, but users may or may not be aware that this path through the task flow exists, hence a selection is needed.

Benefits, Advantages and Disadvantages

Advantages

• GOMS is one of the few models of human-computer interaction that is based on solid research.

• GOMS allows analysts to benchmark and compare the user efficiency of multiple interfaces. This includes comparisons to a system that hasn’t been built yet.

• GOMS can be used to estimate cost savings associated with increased user performance.