Statistics Meeting Book (May 15, 2019)

ANNEX E Example of Graph of POD Values from Qualitative Method Single Laboratory Data Figure X? . Example of Graph of POD Values from Qualitative Method Single Laboratory Data

Notes : ( 1 ) The concentration plotted should be MPN/test portion. ( 2 ) Confidence intervals may also be plotted. ( 3 ) Collaborative data should be plotted analogously.

ANNEX F Calculation of LPOD and dLPOD Values from Qualitative Method Collaborative Study Data For a multilaboratory trial where L = number of laboratories, R = replicates per laboratory, N = LR = total replicates, LPOD estimate is given by LPOD , Where is the number of positive results. x x N Method for estimating LPOD 95% confidence intervals: Step 1. —Enter data into AOAC spreadsheet with 1 for positive response and 0 for negative response. Record the mean LPOD, s(R), and s(r). Step 2 .—Calculate s(L), standard deviation due to laboratory effect as:

2 ( ) ( ) s L s R s r ( )

2

Step 3 .—Calculate s(POD) as the standard deviation of the individual laboratory POD estimates.

¦

2

(

)

i POD LPOD

( s POD

)

1

L

Step 4 .—Calculate degrees of freedom, df for s(POD) as follows:

df = L-1

Step 5 .—Calculate 95% confidence limits on LPOD: If 3 ” x ” N-3:

( s POD

)

t

½ ¾ ¿

0.975,

df

max 0, ®

LCL

LPOD

L

¯

( s POD

)

t

½ ¾ ¿

0.975,

df

min 1, ®

UCL

LPOD

L

¯

If [ ” RU 1-[ ” :