Task Analysis (HTA)
- Task analysis is used mainly to investigate an existing situation, not to envision new systems or devices. It is used to analyze the underlying rationale and purpose of what people are doing: what are they trying to achieve, why are they trying to achieve it, and how are they going about it?
- The information gleaned from task analysis establishes a foundation of existing practices on which to build new requirements or to design new tasks.
- Task analysis is an umbrella term that covers techniques for investigating cognitive processes and physical actions, at a high level of abstraction and in minute detail.
- Practice, task analysis techniques have had a mixed reception. The most widely used version is Hierarchical Task Analysis (HTA)
Hierarchical Task Analysis (HTA)
Hierarchical Task Analysis (HTA) was originally designed to identify training needs (Annett and Duncan, 1967). It involves breaking a task down into subtasks and then into sub-subtasks and so on.
HTA focuses on the physical and observable actions that are performed, and includes looking at actions that are not related to software or an interaction device at all.
The starting point is a user goal. This is then examined and the main tasks associated with achieving that goal are identified. Where appropriate, these tasks are subdivided into subtasks.
Consider the library catalog service, and the task of borrowing a book. This task can be decomposed into other tasks such as accessing the library catalog, searching by name, title, subject, or whatever, making a note of the location of the book, going to the correct shelf, taking it down off the shelf
This set of tasks and subtasks might be performed in a different order depending on how much is known about the book, and how familiar the user might be with the library and the book's likely location.
Note how the numbering works for the task analysis: the number of the plan corresponds to the number of the step to which the plan relates. For example, plan 2 shows how the subtasks in step 2 can be ordered; there is no plan 1 because step 1 has no subtasks associated with it.
An alternative expression of an HTA is a graphical box-and-line notation.
Here the subtasks are represented by named boxes with identifying numbers. The hierarchical relationship between tasks is shown using a vertical line. If a task is not decomposed any further then a thick horizontal line is drawn underneath the corresponding box.