Page 200 - Safety Risk Management for Medical Devices

CHAPTER 21

On Testing

Abstract
Testing, in general is not a Risk Control. Rather, testing helps identify errors in design or implemen-
tation. Testing can also be used to build confidence in the design choices, and verify the imple-
mented Risk Controls. One of the benefits of risk management is to provide a basis for risk-based
sample-size determination for testing. This in turn can help steer resources toward the safety-critical
aspects of the System.
Keywords: Testing; Risk Control; sample size; confidence; reliability

Testing can show the presence of errors, but not their absence.
Edsger Dijkstra, computer scientist (May 11, 1930 2002)
Testing, in general is not a Risk Control. Rather, testing helps identify errors in
design or implementation. Testing can also be used to build confidence in the design
choices, and verify the implemented Risk Controls. An exception to this is when test-
ing is used to eliminate faulty products from reaching the market. For example, qual-
ity control (QC) testing at the end of the manufacturing process may be able to
detect and reject products that have a safety defect. This type of testing does not elim-
inate the Hazard, but does eliminate exposure to the Hazard, and therefore it influ-
ences the P 1 .

21.1 TYPES OF TESTING

During the course of product development, many types of testing are employed.
Below, a few examples that are relevant to Risk Management are cited.

• Concept testing
This type of testing is done to gain insights into the physics of operation of the
medical device. It can demonstrate the feasibility of a concept, and give insights
into Failure Modes. This type of testing can support assertions of failure Occ
ratings. Concept testing is sometimes confused with mitigations, or Risk
Controls. It is not the same. Testing doesn’t reduce the rate of occurrence of a
failure—it only supports the assertion of Occ rating.

Safety Risk Management for Medical Devices r 2018 Elsevier Ltd.
DOI: https://doi.org/10.1016/B978-0-12-813098-8.00021-0 All rights reserved. 179