Methodology I: Task Analysis - Foundations for Designing User-Centered Systems - page 310

you did not expand the hierarchy down a level. You then multiply these together to
get the stopping value: if this is acceptable, then you terminate the analysis
(Kirwan and Ainsworth 1992 ).
11.3.3 Summary
The main advantage of HTA is that, when carried out correctly by a skilled
analyst, it can provide useful information to inform design relatively quickly. It
does not require the interface or the interface details to be fully specified, so it can
be used during the early stages of system development. Once created, the analysis
can be extended, using appropriate methods to provide further details on the
cognitive aspects of the task. HTA's main disadvantage is that the way in which its
results are usually presented do not map readily onto the representations used by
software engineers. Either the task analyst or the system developer will probably
have to carry out further work to translate the results of the HTA into something
that can be used during development.
11.4 Cognitive Task Analysis
As the nature of work in many domains moved from mostly manual control to
mostly monitoring and supervisory control—sometimes described as a change
from doing to thinking—it became increasingly important to take account of the
cognitive aspects of work. Rather than pulling levers, opening and closing valves,
the users now spent most of their time tracking the behaviour of a computer-based
system on a display screen, making decisions and interacting with the system using
the relevant input devices (e.g., in aviation many aircraft now employ a joystick
device rather than a control yoke to help fly it).
Cognitive Task Analysis (CTA; e.g., see Schraagen et al. 2000 for an overview)
extends more traditional task analysis techniques to facilitate the collection of
information about the mental processes that underpin observable task performance.
It should be noted that this does not mean that CTA and HTA are mutually
exclusive: normally they should be used to complement one another.
11.4.1 CTA Components
A CTA will usually comprise the application of a set of methods (e.g., Seamster
et al. 1997 discuss a range of methods that can be used in the aviation domain).
One of the first steps in carrying out a CTA is therefore to choose the methods and
tools that are appropriate to the particular situation that is being studied. The
methods that can be used include: