Task Analysis Identifying needs and establishing requirements Task

Task Analysis Identifying needs and establishing requirements

Task analysis • Task descriptions are often used to envision new systems or devices • Task analysis is used mainly to investigate an existing situation • It is important not to focus on superficial activities What are people trying to achieve? Why are they trying to achieve it? How are they going about it? • Many techniques, the most popular is Hierarchical Task Analysis (HTA)

Hierarchical Task Analysis • Involves breaking a task down into subtasks, then sub-tasks and so on. These are grouped as plans which specify how the tasks might be performed in practice • HTA focuses on physical and observable actions, and includes looking at actions not related to software or an interaction device • Start with a user goal which is examined and the main tasks for achieving it are identified • Tasks are sub-divided into sub-tasks

e l p exam 0. Hierarchical Task Analysis In order to borrow a book from the library 1. go to the library 2. find the required book 2. 1 access library catalogue 2. 2 access the search screen 2. 3 enter search criteria 2. 4 identify required book 2. 5 note location 3. go to correct shelf and retrieve book 4. take book to checkout counter

e l p exam Hierarchical Task Analysis (plans) plan 0: do 1 -3 -4. If book isn’t on the shelf expected, do 2 -3 -4. plan 2: do 2. 1 -2. 4 -2. 5. If book not identified do 2. 2 -2. 3 -2. 4.

e l p exam Hierarchical Task Analysis (graphical) Borrow a book from the library 0 plan 0: do 1 -3 -4. If book isn’t on the shelf expected, do 2 -3 -4. go to the library 1 find required book 2 retrieve book from shelf 3 take book to counter 4 plan 2: do 2. 1 -2. 4 -2. 5. If book not identified from information available, do 2. 2 -2. 3 -2. 4 -2. 5 access catalog 2. 1 access search screen 2. 2 enter search criteria 2. 3 identify required 2. 4 book note location 2. 5

Predictive models • Provide a way of evaluating products or designs without directly involving users • Psychological models of users are used to test designs • Less expensive than user testing • Usefulness limited to systems with predictable tasks - e. g. , telephone answering systems, mobiles, etc. • Based on expert behavior

GOMS (Card et al. , 1983) • Goals - the state the user wants to achieve e. g. , find a website • Operators - the cognitive processes & physical actions performed to attain those goals, e. g. , decide which search engine to use • Methods - the procedures for accomplishing the goals, e. g. , drag mouse over field, type in keywords, press the go button • Selection rules - determine which method to select when there is more than one available

Keystroke level model GOMS has also been developed further into a quantitative model - the keystroke level model. This model allows predictions to be made about how long it takes an expert user to perform a task.

e l p m exa Response times for keystroke level operators (Card et al. , 1983)

Summary • Task analysis techniques such as HTA help to investigate existing systems and practices • Predictive models are used to evaluate systems with predictable tasks such as telephones. • GOMS, Keystroke Level Model, & Fitts’ Law predict expert, error-free performance.