PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26GOMs and Action Analysis and more1. GOMS2. Action Analysis•Quantitative analysis important in early design–performance, error rate, learnability•Use GOMS and action analysis to predict task performance with interactive systems–no implementation required•Perform GOMS and action analysis on low-fidelity prototypes or existing applications–assumes error-free, goal-directed, rational behaviorBig PictureAnalysis Early Design Late Design Implementation DeploymentGoalsMethodsArtifactsExplore design spacePaper prototypesTask scenariosRefine selected designEmpirical studyUI guidelinesFunctional testFunctional prototypeImplement and integrateEmpirical studyUI guidelinesFunctional testFunctionalinterface & systemGather requirements for next releaseField studyCritical incident walkthroughsInterviews and surveysUsability reportContextual inquirySurveysObservationsInterviewsTask analysisUser descriptionsAffinity diagramsDesign briefTask descriptionsIdentify:Usability goalsContentUsers & tasksSketching & brainstormingCognitive walkthroughGOMSHeuristic evaluationAction analysisContext of TCUID - Task Centered User Interface DesignTask Performance•Task performance is critical in–airline and automobile displays–emergency management systems–process control systems–customer service systems and more•Should measure task performance early to–minimize task performance on high-frequency tasks–select among alternative designs–ensure that critical performance goals will be satisfied–cost justify replacement of an existing systemReal-World Example•For every second saved in operator support, a company could save 3 million dollars per year–NYNEX estimate for its operator support, [Gray et al., GOMS Meets the Phone Company, Interact, 1990]•Replace old workstations with new workstations–promised to reduce operator support time by 2.5s–weigh against investment of the new systems (about 1000 workstations at $10,000 each)•Conduct empirical study to compare operator performance on old and new systems•Perform GOMS analysis to help explain resultsFindings•Operators slower on new workstations–would have cost another $3 million per year•GOMS analysis showed that an operator had to perform more operations along the critical path for the new systems–GOMS is a predictive and explanatory modelGOMS•Goals: what a user wants to accomplish•Operators: mental or physical actions that change the state of the user or system•Methods: groups of goals and operators•Selection rules: determine which method to apply, if more than one availableGOMS•A method to describe tasks and how a user performs those tasks with a specific design–bridges task analysis with a specific interface design–error-free, goal-directed, and rational behavior•Views humans as information processors–small number of cognitive, perceptual, and motor operators characterize user behavior•To apply GOMS:–analyze task to identify user goals (hierarchical)–identify operators to achieve goals–sum operator times to predict performanceGOMS Can Be Used To:•Develop task-centered documentation•Predict time to learn how to perform tasks•Predict likelihood of errors•Predict time to perform tasks–predictions tied to specific interface designsApply GOMS When•Want a formal method of writing tasks–enables you to identify intersections across tasks, but requires a consistent vocabulary–generates discussion (concrete representation)–matches tasks to specific interface design•Want to make tasks more efficient–or just the repetitive parts of larger tasks–even creative tasks have repetitive partsJohn, B.E. 1995Who Can Use GOMS•Just about everyone–formal training not required; experience helps•Have multiple people perform analysis and compare results–results are often surprisingly consistentHow To Use GOMS•Analyze hierarchical structure of a task –coarse analysis focuses more on the cognitive structure of a task–fine analysis focuses more on the structure imposed by the specific interface design•Analyze alternative methods•Assign operators to base level goals•Assign times to operators•Sum the operator timesOperator TimesPress key on keyboard280 msUse mouse to point to object on screen1500 msMove hand to pointing device300 msMove eyes to location on screen230 msRetrieve item from memory1200 msLearn a single step in a procedure25 secondsSelect among methods1200 msMore available in TCUID chapter 4GOMS Example•Retrieve the article entitled “Why Goms?”–written by Bonnie John, 1995, in ACM DLGoal Structure•Goal: Retrieve article from ACM DL–Goal: Go to ACM •Goal: Enter ACM URL•Goal: Submit URL–Goal: Go to DL•Goal: Locate DL link•Goal: Select the link–Goal: Select method•[Method: Search method•Goal: Search for article–Goal: Enter search parameters–Goal: Submit search–Goal: Identify article from results•Goal: Select the article]•[Method: Browse method - <take home exercise>]–Goal: Save article to disk•Goal: Initiate save action•Goal: Select location•Goal: save article to that locationCan GOMS Be Trusted?•Predictions made by GOMS models validated in many research studies–assumes that you have a valid model!•Build initial model based your own understanding of a task’s execution–record other users performing the task–compare predicted versus actual sequence–refine and iterateGOMS Worth the Effort When•Want quantitative estimates of human performance without having to–build a working system–train people to use the system to measure performance–measure performance for many usersGOMS: Pros and Cons•Pros–predict human performance before committing to a specific design in code or running empirical studies–no special sills required–many studies have validated the model (it works)•Cons–assumes error-free, skilled behavior–no formal recipe for how to perform decomposition–may require significant time investmentIn-Class Exercise•Perform a GOMS analysis for a task that your initial interface design supportsAction Analysis•Write down each step that a user must perform in your interface to achieve a task•Multiple number of steps by [2, 3] secs–provides range of [best, worst]
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