Methodology I: Task Analysis - Foundations for Designing User-Centered Systems - page 307

created to perform a set of five tasks using a particular cell phone. The tasks
were to adjust the ringer volume, access the tip calculator, view all contacts,
view the date, and access the web browser. The resulting model was used to
predict how long it would take to perform the five tasks with a cell phone and
its initial menu structure. When compared with data from five practiced users
the predictions turned out to be fairly accurate, but also showed where there was
room for improvement in the design of the menus. The model suggested that
reordering the menus to put the most often used menu items first would save
about 30% of the total interaction time.
5. To create user manuals. The results of the TA show in detail the steps that are
involved in carrying out a task. User manuals can be created by translating this
into text and elaborating, where appropriate. Basing the manual on a task
analysis helps to make the manual more accurate, and more acceptable to the
users, particularly if the TA was used to analyze how users really did the tasks.
Closely related to the idea of user manuals is the notion of training people to do
the task. In safety critical systems, for example, you want all the users to do the
same task in (more or less) the same way. A TA can be used as the basis for
developing standard operating procedures (which are used in domains other than
safety critical systems too). In addition, because the TA shows the knowledge that
is required to carry out particular tasks, it becomes possible to compare what the
users know with what they need to know. Where any gaps are identified, this
suggests where training could be useful to increase the users' knowledge to the
appropriate levels.
11.3 Hierarchical Task Analysis
Hierarchical Task Analysis (HTA) is probably the most widely used method in
human factors and ergonomics. An initial HTA is often a precursor to the use of
other methods, largely because it provides details about task activity. The precise
level of detail depends on the depth of the analysis, which is determined by the
original purpose of the analysis. Like most methods of task analysis, HTA takes a
decompositional approach.
11.3.1 HTA Components
HTA involves decomposing goals into subgoals (Annett 2005 ), although it is often
described in terms of decomposing tasks into subtasks. The order and structure of
these goals and subgoals is represented visually. The analysis is usually presented
either as a hierarchical graph structure, or in a tabular textual format. Each goal
(and subsequent subgoals) will be accompanied by a plan. These plans, which