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The POD estimate was calculated as the number of positive outcomes divided by the total
1
number of trials. Estimations were made for the POD with a 95% confidence interval for
2
the candidate method, the reference method and, if included, the presumptive and
3
confirmed results.
4
Difference of Probabilities of Detection (dPOD) were also calculated.
5
The dPOD
CP
was estimated as the difference between the candidate presumptive result
6
POD (POD
CP
) and the candidate confirmed result POD (POD
CC
) values. The 95%
7
confidence interval on the dPOD
CP
was calculated.
8
9
dPOD
CP
= POD
CP
- POD
CC
10
11
The dPOD
C
was estimated as the difference between the candidate method and reference
12
method POD values. The 95% confidence interval on the dPOD
C
was calculated.
13
dPOD
C
= POD
C
– POD
R
14
15
If the confidence interval of a dPOD did not contain zero, then the difference was
16
statistically significant at the 5% level.
17
Results
18
19
Chicken nuggets – 25g
20
For the chicken nugget analysis there were 5 confirmed positives for the LPT method and
21
5 confirmed positives for the USDA reference method. All uninoculated samples were
22
negative with both methods. There were no false positives for the VIDAS method (dPOD
23
= 0, CI: -0.26 to 0.26). There was no significant difference between the LPT method and
24
the reference method using unpaired Chi-square test (
X
2
= 0) or the POD (dPOD = 0, CI:
25
-0.26 to 0.26). See Tables 3, 8, 9 in the Appendix.
26
Pepperoni – 25g
27
For the pepperoni analysis there were 15 confirmed positives for the LPT method and 10
28
confirmed positives for the USDA reference method. All uninoculated samples were
29
negative with both methods. There were no false positives for the VIDAS method (dPOD
30
= 0, CI: -0.26 to 0.26). There was no significant difference between the LPT method and
31
the reference method using unpaired Chi-square test (
X
2
= 2.6) or the POD (dPOD = 0.25,
32
CI: -0.05 to 0.49). See Tables 3, 8, 9 in the Appendix.
33
Hot dogs (beef)
34
For the hot dog analysis there were 6 confirmed positives for the LPT method and 1
35
confirmed positives for the USDA reference method. All uninoculated samples were
36
negative with both methods. There were no false positives for the VIDAS method (dPOD
37
= 0, CI: -0.27 to 0.27). There was a significant difference between the LPT method and
38
the reference method using unpaired Chi-square test (
X
2
= 4.22) and the POD (dPOD =
39
0.25, CI: 0.01 to 0.47). See Tables 3, 8, 9 in the Appendix.
40
51