AAFCO Proficiency Testing Program Statistical Treatment, Reports and Supporting Documents

Documentation: Statistical procedures and approaches.

Here I have provided a pdf presentation in slide form describing the calculations and parameters used to summarize the information from a sample dataset.

AAFCO Reports AAFCO PTP Statistics Documentation.

Documentation: Examples and International Harmonized Protocol

Here are examples of Report Cards and the Master Lists for all the data derived from a single sample as well as the International Harmonized Protocol which is our program guiding document.

AAFCO Reports Example of a Proficiency Test Report Card.
AAFCO Reports Example of an Individual Method Proficiency Test Report Card.
AAFCO Reports Example of an Individual Methods Test Report
AAFCO Reports Example of a Master List for Proficiency Testing
AAFCO Reports Example of a Method Performance Report.
AAFCO Reports The International Harmonized Protocol For The Proficiency Testing Of Analytical Chemistry Laboratories (IHP, 2006).

Documentation: Sample Homogeneity and Stability Evaluation

Here are presentations on sample homegeneity and stability monitoring. Of particular interest is a pseudo homogeneity/stability check we have established for every sample.

AAFCO Reports Homogeneity Monitoring.
AAFCO Reports Stability Monitoringing.

Documentation: Mycotoxin Scheme

For the Mycotoxin Scheme samples are carefully prepared by comminution and quantitatively blending a contaminated feed material with a feed matrix of interest. The finished bulk sample undergoes detailed Mycotoxin analysis by a reference lab including Homogeneity testing. It is then split and distributed to clients for their analysis.

When the program started the Assigned value was provided by a reference lab and not based on the consensus of participants. We quickly learned that the assigned value was occasionaly quite far from the Consensus Value. At the 2015 mid year meeting in San Antonio it was agreed to use the Consensus Value as calculated using robust statistics. The fit-for-purpose standard deviation is derived from a modified Horwitz relationship. The following pdf presentation describes this statistical approach.

AAFCO Reports Mycotoxin Scheme.

The following presentation decribes the January 2015 protocol change to Consensus Value for determing Z scores.

AAFCO Reports Revised Mycotoxin Scheme.

The Following are Examples of Available Reports.

AAFCO Reports Example of a Mycotoxin Scheme Proficiency Test Report Card.
AAFCO Reports Mycotoxin Scheme Example of a Master List for Proficiency Testing.

Documentation: Minerals Scheme

For the Minerals Scheme samples are carefully prepared from prior check sample material. Spike minerals are carefully blended into the base material as described below. The blended batch is then split and distributed to clients for their analysis.

AAFCO Reports Minerals Scheme.

The Following are Examples of Available Reports.

AAFCO Reports Example of a Minerals Scheme Proficiency Test Report Card.
AAFCO Reports Minerals Scheme Example of a Master List for Proficiency Testing.

Related Documents: published by The Analytical Methods Committee of The Royal Society of Chemistry (AMC)

Here I have provided some selected short supporting documents with emphasis on short. There is a great deal of literature describing the applications of Robust Statistics over an extremely diverse range of subjects. John Tukey, Peter Huber and Frank Hampel have been credited with founding the discipline and all this since the landmark paper by Tukey in 1960. So, you can see that this is a fairly young science nevertheless, the literature and bookshelves are rife with the subject.

AAFCO Reports Analytical Methods Committee 2 page Technical Brief describing the Robust Calculations used in the IHP and ISO 13528.
AAFCO Reports Analytical Methods Committee 2 page Technical Brief on representing data distributions with kernel density estimates.
AAFCO Reports Analytical Methods Committee 2 page Technical Brief describing and using the "Fitness for Purpose" criterion.
AAFCO Reports Analytical Methods Committee 2 page Background Paper "What is proficiency testing?"
AAFCO Reports Analytical Methods Committee 2 page Technical Brief describing Creating your own ffp criteria.
AAFCO Reports Analytical Methods Committee 5 page report on "Robust Statistics - How Not to Reject Outliers", 1989
AAFCO Reports Analytical Methods Committee 2 page Technical Brief on "The amazing Horwitz function"

Interesting Articles:

AAFCO Reports Short 3 page philosophical description of Robust Statistics by Frank Hampel (2001).
AAFCO Reports Short 3 page description of the historical development of Robust Statistics by Elvezio Ronchetti (2006).
An Introduction to Robust Measures of Location with some nifty apps to model and view contaminated Normals.

Selected Reading: The following are a few pertinent references to which I can not provide open access.

"Robust Estimation and Hypothesis Testing", 2nd Ed., Rand R. Wilcox, 2005, Elsevier

"Robust Statistics", 2nd Ed., P.J. Huber and E.M. Ronchetti, 2009, Wiley

"Robust Statistics: The Approach Based on Influence Functions", F.R. Hampel, E.M. Ronchetti, P.J. Rousseeuw and W.A. Stahel, 1986, Wiley

"A survey of sampling from contaminated distributions", J.W. Tukey, (1960). In "Contributions to Probability and Statistics.", I. Olkin, S.G. Ghurye, W. Hoeffding, W.G. Madow and H.B. Mann (Eds), Stanford University Press, pp. 448485.





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