Task Analysis

1. Task Analysis CSCI 4800/6800 Feb 27, 2003

2. Goals of task analysis • Elicit descriptions of what people do • Represent those descriptions • Predict difficulties, performance • Measure learnability, transfer of knowledge between systems • Evaluate systems against usability and/or functional requirements

3. Possible problem with TA • Instantiate current tasks in new system, rather than redesigning flow of work to achieve desired higher-level function …

4. Lower-level view: • Actions/operations: • Pressing a key • Moving a mouse

5. Types of TA techniques: • Focus on: • Cognition • Practice of task • Logic of task

6. Goals, tasks, actions : terminology • Goal = external task, such as producing a letter • Device = method, tool, or technique appropriate for achieving goals • Tasks = activities necessary to achive goals using a device • Subtasks = components of tasks • Actions = simple tasks w/ no control structure • Method = plan = number of tasks or actions linked into a sequence

7. Types of Task Analysis • Hierarchical Task Analysis (HTA) • Cognitive Task Analysis • Modeling “how to” knowledge

8. HTA: Hierarchical Task Analysis • Graphical representation • Decomposition of high level task into constituent subtasks, operations, plans • Uses structure chart notation

9. Structure chart notation • activities ordered left to right • * indicates iteration • ○ indicates selection • ----- indicates absence of an action

10. Creating an HTA diagram: • Start the analysis • Progress the analysis • Finalize the analysis

11. Starting the Analysis • Define the area of work / main task • Break down main task into 4-8 subtasks; specify subtasks in terms of objectives • Draw subtasks as layered plans

12. Progressing the analysis • Choose level of detail • “click mouse” v. “delete block of text” • Choose depth-first, breadth-first, or combo • Use hierarchical numbering convention 1, 2, 3, then 1.1, 1.2, 1.3 and so on ...

13. Finalizing the analysis • Check for consistency in decompositions and numbering of tasks • Consult with user knowledgeable in task domain

14. Cognitive Task Analysis • Inform the design process through application of cognitive theories • Some tasks, actions are cognitive – define these • Examples: • decide which button to press • recall previously stored knowledge from memory • compare two objects • Model the internal representation and processing that occurs for the purpose of designing tasks that can be undertaken more effectively by humans

15. Techniques for CTA • MHP – Model Human Processor (Card ’83) • Psychological model of humans as three interacting systems: perceptual, motor, cognitive. Each system has its own memory and processor. • GOMS – Goals, Operators, Methods, and Selection Rules, and related NGOMSL(Kieras, ’88) • CCT – Cognitive Complexity Theory

16. Techniques for CTA • TKS – Task Knowledge Structures (Johnson ’92) • Theory: Assumes that as people learn and perform tasks, they develop knowledge structures • KAT – Knowledge Analysis of Tasks (Johnson ’92) • Method: identify the elements of knowledge represented in a task knowledge structure

17. Other techniques … • Focus on learnability (Task-Action Grammars) • Focus on mappings from external tasks to internal tasks (External Task Internal Task, Yoked State Spaces)

18. Modeling Procedural Knowledge • “how to do it” knowledge • Focuses on task to action mapping • GOMS (Goals, Operations, Methods, Selection Rules) is most famous approach

19. The GOMS approach • Three levels of granularity: • GOMS model (general approach fo accomplishing set of tasks) • unit task level : breaks users’ tasks into unit tasks, then estimates the time it takes for user to perform these • keystroke level: describes and predicts time it takes to perform a task by specifying the keystrokes needed.

20. Exercise w/ GOMS • In a word processor, a single word can be selected by double-clicking the cursor in the middle of the word. If the user wishes to select an arbitrary string of characters, the characters must be highlighted by dragging the mouse over the text with the mouse button held down. To cut the text out of a document, the user must first highlight the text and then issue the cut command. • Write an NGOMSL description for the goal of ‘cut out text’. • Write out the selection rules for this example • Write out the method for selecting a word and for selecting an arbitrary string of characters

21. Uses of GOMS models • to predict quality of existing system or prototype • to check of consistency of methods (similar goals are achieved by similar methods) • to check that most frequent goals are achieved by relatively quick methods • as a quantitative evaluation technique • to choose between alternative designs

22. Problems with GOMS • works well for simple tasks, unwieldy for larger tasks • requires substantial time, skill, effort • results questioned by some

23. Representing task knowledge • Important to understand what people already know about the specific task and this class of tasks • Now: focus on goal-to-task mapping • “KAT” – knowledge analysis of tasks, looks at this

24. More recently... • focus has shifted to less formal methods • claims analysis[Carroll & Kellogg, 89] • Scenario analysis[Young & Barnard, 91; Carey 91] • Cognitive walkthroughs[Lewis, 90] • Design rationale [Carroll and Moran 91; Maclean 91] • “cognitive dimensions” framework [Green 89]

25. Cognitive Dimensions • Vocabulary for describing aspects of information structures: • Viscosity • resistance to change. How easy is it to make changes to some aspects of the artifact? • Delayed gratification • effort required to meet goal. • Premature commitment • user is forced to make choices too soon • Hidden dependencies • information links that aren’t easily visible

26. ERMIA -- • Entity Relationship Modeling for Information Artifacts • Uses ER notation • One for conceptual level • One for perceptual level

27. ERMIA – example: hidden dependecy Spreadsheet cell Spreadsheet cell 1 1 uses M 1 uses used by M M Related cell Related cell conceptual level perceptual level Highlights problem w/ spreadsheets – not visible which cells use this cell, only which cells are used by this cell

28. Exercise • Draw an ERMIA diagram for the case of Word ‘style sheets”, based on the following description: • A style is a collection of character and paragraph formats that can be applied to paragraphs or documents as required. A style can be based on another style. For example, the styles ‘List’ and ‘Quotation’ may be based on the style ‘Normal’. Changing style Normal will change all styles based upon it. The style display shows only the style that it is based upon.

29. Summary • Task analysis describes behaviors at three levels: goals, tasks, actions • Tasks are usually viewed in terms of a hierarchical decomposition of tasks into subtasks. • HTA and related techniques focus on what actually happens, rather than on what should happen.

30. Summary, continued • Cognitive task analysis techniques aim to describe some aspect of the cognitive characteristics of users’ tasks. • Some methods (such as GOMS) concentrate on users’ procedural or “how-to-do-it” knowledge. • Other methods focus on task knowledge. • Many techniques difficult to use / don’t scale well.