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NJ-DEP PT Roundtable Statistical Overview College of New Jersey February 26, 2004

NJ-DEP PT Roundtable Statistical Overview College of New Jersey February 26, 2004. Mike Blades/Mark Carter/Shawn Kassner Environmental Resource Associates. Statistical Analyses of Study Data. Proficiency Testing Limits . Limits are based on

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NJ-DEP PT Roundtable Statistical Overview College of New Jersey February 26, 2004

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  1. NJ-DEP PT RoundtableStatistical OverviewCollege of New JerseyFebruary 26, 2004 Mike Blades/Mark Carter/Shawn Kassner Environmental Resource Associates

  2. Statistical Analyses of Study Data

  3. Proficiency Testing Limits • Limits are based on • USEPA National Standard Criteria Document, Dec. 1998. • NELAC Fields of Testing tables. • ERA historically based statistical limits, approved by NJ-DEP for each study.

  4. Proficiency Testing Limits • WP and WS study limits are primarily: • Regression equations. • Fixed percentage limits. • Soil study limits are based on  3 standard deviations around the study mean.

  5. PT Statistical Review Per NELAC Chap. 2 Appendix C, Section C.4 PT Providers are required to use “robust” statistical analyses for: • Bi-modal or multiple-modal distributions • Method biases • Reporting anomalies

  6. PT Statistics – Study Data • Study Data Review • Examine the study data vs. method/technology • Examine the study data vs. date of analyses • Examine the study data distribution

  7. PT Statistics – Mean Analyses • Mean analyses • Compare the study mean to: • Predicted mean from the USEPA/NELAC criteria • ERA analytical verification and stability mean • ERA historical sample design mean

  8. PT Statistics – Standard Deviation • Standard deviation analyses • Compare the study standard deviation to: • Predicted standard deviation from the USEPA/NELAC criteria • ERA historical standard deviation

  9. PT Statistics – Pass/Fail Rates • Pass/Fail rate analyses • Compare the study pass/fail rate to: • USEPA historical pass/fail rates • ERA historical pass/fail rates

  10. PT Statistics – Study Acceptance Limits • Final Study Acceptance Limits analyses • Compare USEPA/NELAC criteria based acceptance limits to: • Calculated statistical study based limits • ERA historically based calculated limits • Look for anomalies between the limits

  11. Study Discussion • If the any of the following indicate an issue that may impact the study evaluations, that standard/analyte is investigated: • Study Mean • Study Standard Deviation • Pass/Fail Rates • Acceptance Limits • With the results of the investigation are reported to each study participant, each regulatory agency, and to NIST and A2LA.

  12. Reporting Statistical Data and VHS Results • VHS testing data and study statistics reviewed together to ensure reliability of the study for every analyte. • All of the VHS testing data and study statistics are available to every participant and accrediting agency via ERA’s eDATA site.

  13. WHY? • We do all this for three reasons: • Remove uncertainty from the performance evaluation of the laboratory. • Demonstrate the efficacy of the PT standards and the evaluations of the laboratories’ performance. • The NIST, NELAC and NJ-DEP documents require us to.

  14. Thank You! Mike, Mark & Shawn 800-372-0122 www.eraqc.com mblades@eraqc.com skassner@eraqc.com

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