# GOMS Model GOMS (Goals, Operators, Methods, and Selection rules) is a cognitive task analysis model for predicting how long expert users take to complete tasks with a computer system. Developed by [[Stuart Card]], [[Thomas P. Moran]], and [[Allen Newell]] and published in *The Psychology of Human-Computer Interaction* (1983), GOMS was one of the first rigorous engineering models for [[Human-Computer Interaction (HCI)]]. GOMS analyzes tasks by decomposing them into hierarchical goals, primitive operators (physical and mental actions), methods (sequences of operators), and selection rules (how users choose between methods). By assigning time values to operators, designers can predict task completion times before building interfaces. This enables comparison of design alternatives and identification of efficiency improvements without extensive user testing. ## Components | Component | Description | Example | |-----------|-------------|---------| | **Goals** | What the user wants to accomplish | "Delete a word" | | **Operators** | Basic actions (physical or mental) | Keystroke, mouse click, mental preparation | | **Methods** | Sequences of operators to achieve goals | Select word → Press Delete | | **Selection Rules** | How users choose between methods | "If hands on keyboard, use Ctrl+D; else use menu" | ## Operator Time Values (KLM) The Keystroke-Level Model (KLM), a simplified GOMS variant, assigns average times: | Operator | Symbol | Time | |----------|--------|------| | Keystroke | K | 0.2 sec | | Point with mouse | P | 1.1 sec | | Home hands to keyboard/mouse | H | 0.4 sec | | Mental preparation | M | 1.35 sec | | Button press (mouse) | B | 0.1 sec | | System response (wait) | R | varies | ## Example Analysis **Task**: Bold a word using keyboard shortcut ``` Goal: Bold selected word Method: Keyboard shortcut Operator: M (mentally prepare) 1.35s Operator: K (Ctrl key) 0.2s Operator: K (B key) 0.2s ───────────────────────────────────── Total: 1.75s ``` **vs Menu method**: ``` Goal: Bold selected word Method: Menu Operator: M (mentally prepare) 1.35s Operator: H (hand to mouse) 0.4s Operator: P (point to Format menu) 1.1s Operator: B (click) 0.1s Operator: P (point to Bold) 1.1s Operator: B (click) 0.1s ───────────────────────────────────── Total: 4.15s ``` Keyboard shortcut is 2.4 seconds faster per use. ## GOMS Variants | Variant | Description | |---------|-------------| | **KLM** | Keystroke-Level Model — simplified, quantitative | | **CMN-GOMS** | Original Card-Moran-Newell version | | **NGOMSL** | Natural GOMS Language — more structured notation | | **CPM-GOMS** | Cognitive-Perceptual-Motor — parallel processing | ## Strengths - Quantitative predictions without user testing - Compare design alternatives objectively - Identify inefficiencies in task flows - Applicable early in design process ## Limitations - Assumes expert, error-free performance - Doesn't model learning, errors, or fatigue - Limited to routine cognitive tasks - Requires skilled analyst ## References - Card, Moran, & Newell (1983). *The Psychology of Human-Computer Interaction* - https://en.wikipedia.org/wiki/GOMS - https://www.interaction-design.org/literature/topics/goms-model ## Related - [[Stuart Card]] - [[Thomas P. Moran]] - [[Allen Newell]] - [[Human-Computer Interaction (HCI)]] - [[Usability]] - [[Cognitive Psychology]]