Errors: An Inherent Part of Human-System Performance - Foundations for Designing User-Centered Systems - page 296

identify the list of functions that the system has to perform. These functions are
then allocated to either the human or the machine using a static approach that is
often based on Fitts' ( 1951 ) list, which is also referred to as the MABA-MABA
(Men Are Better At-Machines Are Better At) approach. The problem with this
approach is that designers often allocate all the tasks that they know how to
automate to the technology, and then leave the human to carry out all the others. If
we want to allocate functions effectively we need to consider the processing
characteristics of both the humans and the technology so that we can reduce the
chances of errors whilst performing a particular function.
If your system requires a lot of functions to be carried out in the same time
frame, you may overload the operator (and the technology), thereby increasing the
chances of an error occurring. In this case you may want to consider whether you
can allocate functions dynamically, allowing tasks to be shed, and reallocated as
workloads change. So, if operators get really busy, it should be possible for them
to hand off tasks to the automation to reduce their workload, thereby improving
overall system performance, and vice versa.
One of the ironies of automation (Bainbridge 1987 ) is that the more complex
socio-technical systems become, the more we rely on people to intervene to fix
them when errors occur. You will therefore often hear people talking about the
need to keep people in the loop. It is important that the users are kept aware of
what the system is doing, by providing them with feedback about the system's
state. They can use this to detect errors, and to update their own mental model of
how the system is working. It is also important that users are given the opportunity
to practice their skills, so they do not forget how to carry out particular tasks,
especially those that they perform infrequently. This is one of the reasons why
aircraft pilots have to undergo recurrent training, and are expected to hand fly their
aircraft on a fairly regular basis.
10.6 Summary
Human error is a complex subject, for several reasons:
• Confusion over the term itself, which gets used to describe the action, the cause
of that action, and the consequence of that action too.
• The same factors govern the expression of both expertise and error.
• Some of the contributors are latent, and lie hidden, waiting for other triggering
or potentiating factors.
• Errors are judgments made in hindsight and require some measure of expected
human performance for comparison.
• Human performance involves a distributed system of people interacting with
technology at the sharp end and organizational elements at the blunt end.
• Decisions made at the blunt end of the system can constrain the way that work is
carried out at the sharp end.