Pooled Prevalence Calculator – Demonstration analyses

Demonstration of freedom using pooled testing with tests of known sensitivity and fixed pool size

This program estimates the confidence that a population is free of disease, or of detecting disease at a specified design prevalence, using pooled testing and assuming a fixed pool size, a test of known sensitivity and 100% specificity and that all pools have a negative test result.

For this analysis, it was assumed that 30 pools of 10 were tested using a test with a sensitivity of 0.9 (90%) and perfect specificity. The design prevalence which we wish to detect is 0.01 (1%) and we require 95% confidence of detecting one or more positives if the true prevalence is greater than or equal to the design prevalence. Input values and results are summarised below:

Input values

 Pool size 

 Number of pools 

 Sensitivity 

 Confidence level 

 Design prevalence 

10

30

0.9

0.95

0.01

 

Results

If all pools test negative, there is 95% confidence that the true prevalence is less than 0.0111.

If all pools test negative, there is 93.28% confidence that the true prevalence is less than 0.01.

For a pool size of 10, a minimum of 34 pools must be tested to provide 95% confidence of detecting a prevalence of 0.01.

The table below lists the number of pools required for various pool sizes to provide 95% confidence of detecting a prevalence of 0.01 and assuming a test sensitivity of 0.9 for all pool sizes.

 Pool size 

 Number of pools 

1

332

2

166

3

111

4

83

5

67

10

34

15

23

20

17

25

14

30

12

40

9

50

7

100

4

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