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Once a design has been realised, it is important to test it to make sure that we have “designed the thing right.” In medical device language, we are verifying how the device performs against technical requirements. These requirements may be functional performance characteristics, dimensional aspects or similar, but are all quantifiable and measurable in some way.

Before design verification testing (DVT), during early phases of the development process, engineering verification testing is often executed to prove an element of the design. This ensures that the concept is developing along the right lines and a thorough job here will save time and money before costly manufacturing decisions are locked in.

Surprises are never appreciated during DVT, so with this in mind, we often recommend a run through of the tests (aka pre-DVT) and equipment with small sample sizes. This helps understand how long the tests take and often unearths new insights into the design or the tests. To further this confidence, the test methods and equipment used for DVT should be robustly checked for suitability. 

Formal DVT is conducted on products that are representative of the final assembled product. This means the results of testing can be used with confidence to make conclusions about the finished design.

Another key aspect of DVT is assessing the sample size to be tested. Unfortunately, there isn’t a magic number which ensures a sample size is large enough to ensure sound conclusions. Considerations such as whether the data is continuous or attribute, the cost of sampling and the sensitivity of making the wrong judgement need to be made. Often standards specific to the product type will help inform this decision. For example BS EN ISO 20072:2013 “Aerosol drug delivery device design verification” provides detailed guidance on the confidence levels required – which inform the sample size planning.

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