Introducing User-Centered Systems Design - Foundations for Designing User-Centered Systems - page 13

contributory factors. In addition to problems with the technology and safety
interlocks, the system (including the technician) was poorly prepared to deal with
typing mistakes by the technician, and in many installations the level of feedback
from the Therac to the radiation technician was not sufficient to help them catch the
mistakes sooner.
1.3.4 Cost 1: Understanding the Users Does Not Guarantee
Success
Although improving the usability of a system can save lives, lead to product
success, and save money, usability is neither a necessary nor sufficient condition
for success, nor is it a protection against loss of money or life. Systems with poor
usability can still be successful for a variety of reasons. For example, they may
offer a functionality that is unique and useful. The earliest versions of planes,
computers, printing presses, and satellite phones were all difficult to use, but
successful because of their unique functionality.
Products that are well designed with the user in mind may still not be successful.
Most or all aspects must be right for a product or system to succeed. Making the
usability right does not make the time to market right, it does not make the price
appropriate, and other critical aspects such as reliability or marketing may fail.
The system also has to be acceptable to the users. The interface may be well
designed on a local level, but if it clashes too much with existing practice (even if
the new system is correct) it can quickly fall into disuse (e.g., see Baxter et al.
2005 ). Similarly, if management does not appropriately support the transition to
the new system, it may also fall into disuse. Glashko and Tabas ( 2009 ) argue that
to understand success you need to understand the user, the business model, and the
technology.
The lack of usability can be a sufficient reason for failure and this is sometimes
overlooked. For some systems, however, usability is not the biggest risk to suc-
cess. Indeed there are many factors that contribute to success, and none of them on
their own are necessary or sufficient to guarantee success. Pew and Mavor ( 2007 )
suggest taking a risk driven spiral-based approach to development to deal with
this; we describe this approach later in the topic.
1.3.5 Cost 2: Knowing When to Stop Analyzing the Users can
be Difficult
Knowing when you should stop analyzing the users and start building your system
is a difficult problem to address. It is an ongoing issue for HCI (and system design