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NALMA / Laboratory Advisory Committee Meeting June 19, 2003 Paul Sauvé, CLS Tolerances for MUN ?????

NALMA / Laboratory Advisory Committee Meeting June 19, 2003 Paul Sauvé, CLS Tolerances for MUN ?????. Types of Analytical Methods: Reference methods Primary reference methods Secondary reference methods Official methods Routine methods Modified methods Screening methods Rapid methods

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NALMA / Laboratory Advisory Committee Meeting June 19, 2003 Paul Sauvé, CLS Tolerances for MUN ?????

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  1. NALMA / Laboratory Advisory Committee Meeting June 19, 2003 Paul Sauvé, CLS Tolerances for MUN ?????

  2. Types of Analytical Methods: • Reference methods • Primary reference methods • Secondary reference methods • Official methods • Routine methods • Modified methods • Screening methods • Rapid methods • Automated methods • Indirect methods • AND… • There are many different definitions for each.

  3. For typical DHI applications, indirect methods are used. An indirect method must be “calibrated” to agree with a direct (reference) method. FAT: Routine method: Infrared transmission analysis (IR) Reference method: Ether extraction (Mojonnier extraction) PROTEIN: Routine method: Infrared transmission analysis (IR) Reference method: Kjeldahl nitrogen determination

  4. MUN: • Routine method: Infrared transmission analysis (IR) • Reference method: differential pH analysis (CL-10) • AND… • Several “secondary reference methods” are also in use: • Skalar • FIA-Star • ChemSpec

  5. Is it acceptable to have different tolerances for different types of methods? YES Tolerances for reference methods for fat and protein are tighter than for the IR methods. This is normal. The reference (calibration) method MUST be more accurate than the indirect method. The problem we face with MUN testing is that both direct and indirect methods are being used for analysis of routine test samples. Some labs using the more accurate direct methods would like to see tighter tolerances.

  6. Are all of the methods capable of providing valuable information? YES While the validity of the indirect methods has been challenged frequently, there is a market for these services and evidence shows that valuable information is being delivered. If tolerances are to be enforced for MUN testing, parameters will need to be wide enough to include the indirect procedures or separate tolerances should be developed for each of the three main classes of methods. The latter approach is preferred. “FITNESS–FOR–PURPOSE” “USER-CENTRED REQUIREMENTS”

  7. Performance Indicators: Mean Difference: The average difference between reference (target values) and the lab values. MD Standard Deviation of Differences: The population standard deviation of the differences between reference (target values) and the lab values. SDD Neither of these indicators can be used independently.

  8. Typical Data Set:

  9. Can we assign a tolerance for MD only? NO

  10. Can we assign a tolerance for SDD only? NO

  11. So… We need tolerances for both MD and SDD or we need to use a different statistical indicator. x x x x x SDD x x x x x x x MD

  12. If tolerances are assigned for MD and SDD, we can draw a box on the graph. Points inside the box satisfy the tolerances. x x x x x SDD x x x x x x x MD

  13. OR… We can define a new parameter, D which represents the distance from the origin (0,0) on the graph. x x x x x SDD x x x x x D x x MD

  14. If tolerances are assigned for D, we can draw a semi-circle on the graph. Points inside the semi-circle satisfy the tolerances. x x x x x SDD x x x x x x x MD

  15. Calculating D: z x y x2 + y2 = z2 Or z = x2 + y2

  16. x x x x x SDD x x x x x D x x MD D = MD2 + SD2

  17. What next?: • Decide on the performance indicators. • MD and SDD • D • Decide on values for each type of method. • “Level 1 certification” • “Level 2 certification” • Decide how tolerances should be applied. • Specifications must be met in every trial, in 3 of the last 4, …

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