Pooled Prevalence Calculator – Demonstration analyses

Sample size calculation for fixed pool size and perfect tests

This option can be used to calculate the number of pools that need to be tested for various values for pool size, estimated prevalence and desired confidence and precision of the estimate. It assumes fixed pool sizes and a test with 100% sensitivity and specificity.

For this analysis, sample size was calculated to provide 95% confidence of estimating a true prevalence of 0.14 (14%) with a precision of 0.055 (5.5%). This is equivalent to the observed prevalence and precision when 162 samples from little red flying foxes in Queensland were tested individually, with 22 positive results (H. Field, pers com). Input values and summary results are shown below. For a pool size of five, 42 pools would be sufficient to provide the desired precision and confidence in the estimated prevalence.

Input

Value

Prevalence

0.14

Precision

0.055

Confidence

0.95

Pool size

Number of pools

Total number of individual samples

1

153

153

2

83

166

5

42

210

10

33

330

15

36

540

20

46

920

25

64

1600

30

95

2850

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