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I Received A Low PSP Score, What Next?

By Ryan LaQuay, Laboratory & Testing Manager

Posted: October 2014

You just received an e-mail notifying you of low PSP ratings. This means that at least one of your scores was more than two standard deviations from the grand average, or that your laboratory did not submit data. (If you want more information on what ratings mean and how we calculate them, please review Proficiency Sample Ratings: Being Average Has Never Been So Good).

So what do you need to do now? If your laboratory is not AASHTO accredited, and is not seeking accreditation, you are not required by AASHTO re:source to take any action. However, you may want to follow the steps outlined here to better understand why your ratings were low. If you are an accredited laboratory and this is your first time receiving a low rating, then a root cause analysis is required. If it is a repeat low rating on the same test or test property then, in addition to the root cause analysis, a second proficiency sample will have to be tested, and satisfactory ratings recorded, in order to maintain your AASHTO accreditation for that test procedure.

Root Cause Analysis
Every accredited laboratory that receives low ratings must perform a root cause analysis and keep the documentation in their records. Essentially, you need to look back and see what caused the problem that led to the low rating and address it.

When performing your root cause analysis, there are many different factors to consider. You will want to look at every aspect of the proficiency sample testing, from the moment that the sample box was opened until the data was submitted.

  • Watch the technician perform the test. Did they prepare the sample and test it in accordance with the test method and the instructions provided?
  • How about the equipment? Did something come loose or break during testing?  Is all of the equipment in conformance with the test method requirements?
  • Take a look at the recorded data. Was a weight or a reading written down incorrectly? Do the units match what is expressed on the data sheet? Does all of the data recorded match the numbers that were submitted?

As you go through this process, document whatever findings you might come across. You can use your own form or the Proficiency Sample Corrective Action Report we have put together. You must document and retain what corrective actions were taken to resolve the issue. These actions must include finding the actual problem, if possible, addressing it, and then implementing changes so that the issue doesn't reoccur. During your next on-site assessment, your assessor will want to see this documentation.

Extra Proficiency Samples (XPS)
If this is the second time in a row you received low ratings (±1 and 0) on the same test property, then there will be a bit more work involved than just a root cause analysis. For starters, your accreditation related to that specific test method will be suspended. To have your accreditation reinstated, you will have to perform the tests again. You can either wait for the next regularly scheduled round of proficiency samples or order a “blind” extra proficiency sample to test sooner. Your score for the sample must be within two (2) standard deviations of the mean of the blind sample in order to be reinstated for the suspended test method. To order a blind sample, contact your Quality Analyst directly. Once you receive the blind sample, you can email your new results, root cause analysis, and corrective action report to your Quality Analyst.

It is important to remember that an occasional low rating is not the end of the world. However, frequent low ratings should be looked at more closely. Ratings for every test has a corresponding performance chart so you can track any trends that may be occurring.  More information on ratings and performance charts can be found in Proficiency Sample Ratings: Being Average Has Never Been So Good


To recap, if it is your first time receiving a low score on a sample, investigate as to what may have gone wrong, document it, and file it away for your next assessment. If this is the second test in a row with a low score, your accreditation for that test method will be suspended. You can have it reinstated by testing another sample, receiving satisfactory ratings, performing a root cause analysis, and rectifying the problem.

Editor’s Note: This article was updated in June 2016.

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Leave a comment
  1. Lofton | Jun 16, 2017


  2. Ellen Smith | Feb 04, 2017
    Thanks for explaining the whole reason. I got the mail and have been confused by the term Low PSP Score which I don’t have any idea about. And explanation for Root cause analysis helped me a lot to understand the criteria.
  3. Ela | Jan 19, 2017
    I just want to say thanks for your wonderful post, it contains a lot of knowledge and information that I needed right now.
  4. susan betcher | Jan 10, 2017
  5. Kimberly Swanson | Nov 02, 2016

    The AAP will only suspend a laboratory's accreditation for repeated PSP ratings of ±1 and 0. However, if an AASHTO-accredited lab receives a ±2 rating for a given test, they are required to perform a root cause analysis and implement corrective action. 

    More details can be found in the AAP Procedures Manual - http://aashtoresource.org/docs/default-source/publicdocuments/aap-procedures-manual.pdf

    It is good practice for non-accredited labs to perform a root cause analysis and implement corrective action for ratings of ±1, ±2 and 0.

  6. | Nov 02, 2016

    Low rating is 2,1, 0 but here it says:

    "Extra Proficiency Samples (XPS)If this is the second time in a row you received low ratings (±1 and 0) on the same test property, then there will be a bit more work involved than just a root cause analysis"

    If second time, should we worry about two consecutive "2" ratings?

  7. bjohnson@aashtoresource.org | Sep 20, 2016
    You can order an extra sample pair to investigate low ratings.  The cost of those samples is equal to the cost of the samples in the normal round of testing.
  8. Paul.Hanczaryk@dot.nj.gov | Aug 25, 2016
    We received a low rating for the Hot Mix Asphalt Gyratory sample 41/42 but it is the first time so we only have to do a root cause analysis.  Can we still receive a sample of the same material just to help us with our "root cause analysis"?

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