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VIDAS LMX & LPT Collaborative Study
April 19, 2013
OMA-2013-Apr-XXX
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8.0
Analyzing Raw Data
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The resulting data will be analyzed by probability of detection (POD).
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8.1
Probability of Detection (POD) -
POD is the proportion of positive analytical
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outcomes for a qualitative method for a given matrix at a given analyte level or
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concentration. POD is concentration dependent. Please see the revised
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microbiology guidelines
5for complete analysis information on POD calculations.
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8.1.1
Calculate:
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8.1.1.1 Estimate of repeatability - standard deviation (s
r
)
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8.1.1.2 Determine POD values for each matrix and concentration - the
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number of positive outcomes divided by the total number of trials.
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8.1.1.3 Estimate of reproducibility – standard deviation of the laboratory
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POD values (s
POD
) and confidence intervals.
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8.1.1.4 Cross laboratory probability of detection (LPOD) – LPODs by
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matrix and concentration with 95% confidence intervals for
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candidate method (presumptive and confirmed) results.
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8.1.1.5 Difference of cross-laboratory probability of detection (dLPOD) –
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difference probability of detection is the difference between any
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two LPOD values.
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8.1.1.5.1
Estimate dLPOD
C
as the difference between the
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candidate and reference LPOD values, include CIs.
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8.1.1.5.2
Estimate dLPOD
CP
as the difference between the
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presumptive and confirmed LPOD values, include CIs.
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8.1.1.5.3
If the CI of a dLPOD does not contain zero then the
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difference is statistically significant
.
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8.1.1.6 For each matrix, graph POD
R
, LPOD
C
and dLPOD
C
by level with
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95% confidence intervals.
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9.0
Appendices
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9.1
Instructions to Collaborators
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9.2
Test Portion Data Report Form
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9.3
Collaborator Comment Form
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9.4
Study Materials
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9.5
Flow Diagram – Soft Mexican Cheese
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9.6
Collaborator Information Sheet
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AOAC INTERNATIONAL Methods Committee Guidelines for Validation of Microbiological Methods for
Food
and Environmental Surfaces (pre-publication document, 2012) Sharon Brunelle, Robert LaBudde, Maria Nelson,
and Paul Wehling
DRAFT DOCUMENT
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