1. Identifying needs and establishing requirements
Task Analysis
Identifying needs and establishing requirements

2. 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)

3. Hierarchical Task Analysis
Involves breaking a task down into subtasks, then sub-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

4. Hierarchical Task Analysis
example
Hierarchical Task Analysis
0. 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

5. Hierarchical Task Analysis (plans)
example
Hierarchical Task Analysis (plans)
plan 0: do If book isn’t on the shelf expected, do
plan 2: do If book not identified do

6. Hierarchical Task Analysis (graphical)
example
Hierarchical Task Analysis (graphical)
Borrow a book from the library
plan 0: do
If book isn’t on the shelf expected, do
go to the library
find required book
retrieve book from shelf
take book to counter 1 2 3 4
plan 2: do
If book not identified from information available, do
access search screen
enter search criteria
identify required book
access catalog
note location
2.1
2.2
2.3
2.4
2.5

7. 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

8. 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

9. 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.

10. Response times for keystroke level operators (Card et al., 1983)
example
Response times for keystroke level operators (Card et al., 1983)

11. 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.