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15 - 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 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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