Inter-Laboratory Proficiency Testing Result Analysis - z Score or Normalized Error

evg78 · May 18, 2012

Hello Everyone,

Let me start of by saying that this site has been so helpful for our ISO 17025 accreditation process. Thank you for all the information.

We are a testing laboratory getting ready for our very first ISO 17025 audit. I just received the inter laboratory proficiency testing results.

I would like to know what is a preferred statistical analysis, z score or a normalized error (En) determination to present to the accrediting body?

I came across some information that suggested the En determination applies more to calibration labs, while z score is preferred for the testing labs.

Any help would be greatly appreciated.

Best Regards,
Edgar

Ajit Basrur · May 19, 2012

Re: Inter-Laboratory Proficiency Testing Result Analysis - z Score or Normalized Erro

Edgar,

Congratulations and Welcome to the Cove :bigwave:

Its great to hear that the Cove was useful for you and your Laboratory.

The activity is slow during weekends and hence you will get response to your questions next week

Hershal · May 21, 2012

Re: Inter-Laboratory Proficiency Testing Result Analysis - z Score or Normalized Erro

evg78 said:
Hello Everyone,

Let me start of by saying that this site has been so helpful for our ISO 17025 accreditation process. Thank you for all the information.

We are a testing laboratory getting ready for our very first ISO 17025 audit. I just received the inter laboratory proficiency testing results.

I would like to know what is a preferred statistical analysis, z score or a normalized error (En) determination to present to the accrediting body?

I came across some information that suggested the En determination applies more to calibration labs, while z score is preferred for the testing labs.

Any help would be greatly appreciated.

Best Regards,
Edgar

Your source is correct, z-score is for testing, En is for calibration. The documents from APLAC may help clarify that for you. They are PT-001 (calibration) and PT-002 (testing), available at no charge from www.aplac.org

Hence, if you are a test lab, your AB will look at z-score.

Hope this helps.

evg78 · May 21, 2012

Re: Inter-Laboratory Proficiency Testing Result Analysis - z Score or Normalized Erro

Hershal,

Thank you for taking the time to provide an answer. The website was very helpful.

Best Regards,
Edgar

Inter-Laboratory Proficiency Testing Result Analysis - z Score or Normalized Error

evg78

Ajit Basrur

Hershal

Metrologist-Auditor

evg78

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