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216 Safety Risk Management for Medical Devices

A great service from biological evaluation to risk management is providing data,
which allows for more accurate risk estimation, instead of simply assuming the worst-
case outcomes.
Biocompatibility testing can be lengthy and expensive. A sound biocompatibility
strategy can provide the justification to waive certain tests. This strategy could, e.g.,
be based on toxicology information or relevant prior use of materials. This is not
only efficient, but also ethical. In some cases, it may be possible to reduce/eliminate
animal testing by substituting chemical and in vitro testing.

29.3 INTERACTION WITH IEC 62366

IEC 62366 [14] is the Usability Engineering Standard. There are two types of formal
testing that are envisioned in this standard: Formative and Summative. Formative tests
are performed iteratively during the design and development phase, with the intention
to explore the effectiveness of the user interface design and to identify potential use-
failures or misuses. Formative tests typically do not have formal acceptance criteria.
Their goal is to guide the design of the user interface (UI) and achieve a level of qual-
ity that ensures the summative tests will be successful. From the risk management per-
spective, the focus of formative testing is on reducing the likelihood of use-failures
that have the potential for creating Hazards.
Summative tests are performed at the end of user interface development, after
formative tests are completed. The objective of summative tests is to produce objec-
tive evidence that the user interface contribution to safety risks is acceptable.
Summative tests are qualitative investigations where observations can be reported in
simple statistics, e.g., 8 out 10 testers succeeded. Summative tests have formal accep-
tance criteria and can be utilized as a means of verification of effectiveness of Risk
Controls.
Risk Management can inform Usability Engineering vis-a `-vis decisions on the
performance of summative tests. One such contribution is on the identification of
user interfaces that have, or have not, an impact on safety. For safety-related user
interfaces, summative tests need to be performed. The choice of the number of parti-
cipants in a summative test can be informed by Risk Management.
IEC 62366-2 [34] offers equation K.1 as:

n
R 5 1 2 ð12PÞ
where
R is the cumulative probability of observing or detecting a usability problem
P is the probability of a single test participant having a usability problem
n is the number of test participants