U.S. flag

An official website of the United States government, Department of Justice.

DNA - A Prosecutor’s Practice Notebook Inventory

Failed Proficiency Testing by the DNA Analyst

Home  |  Glossary  |  Resources  |  Help  |  Contact Us  |  Course Map

The defense may argue that the state's DNA analyst previously failed a proficiency test and therefore the results cannot be trusted. Like validation, proficiency testing is designed to identify problems in testing that need to be corrected.  Those problems could involve analyst error but they likewise could involve previously unrecognized defects in protocol, sample preparation, screening, maintenance, etc.  The most relevant questions are what the nature of the error was, how it was identified, the correction made, and subsequent performance.  The same is true of past contamination.   

First, the prosecutor must contain the failure (how long ago did the failure occur and has the analyst passed the relevant tests since then).

Second, the prosecutor should discuss whether or not the DNA analyst or lab took any action either to ascertain whether this was an isolated mistake or to change any procedure to prevent future similar mistakes.

Third, the prosecutor should emphasize all the other checks and balances in the testing process.  The prosecutor should do the following:

  • Define and describe the quality assurance controls used in the testing
  • Describe to the jury the other indicia of reliability; for example, the victim's DNA was analyzed correctly
  • Explain to the jury that unlike in blind proficiency testing every "real" case requires another analyst to review the casework for accuracy before the report is released

Back Forward