Sample size calculation for fixed pool size and uncertain sensitivity and specificity

Input Values

  

This program calculates the approximate numbers of pools required for given values for pool size, estimated prevalence and desired confidence and precision of the estimate, assuming fixed pool sizes and a test with uncertain estimates for sensitivity and specificity. See the User Guide for more details. See demonstration analysis

For this option it is not possible to calculate an optimum value for m that minimises the variance of the estimated prevalence (see Sample size for fixed pool size and perfect tests ). Therefore, final selection of pool size and corresponding number of pools is a compromise between pool size and number of pools. To minimise bias, it is better to have more pools of a smaller size, rather than fewer, larger pools.

Input values

Required inputs are the estimated true prevalence, the desired level of precision (or acceptable error) and the desired level of confidence. You also need to enter point estimates of test sensitivity and specificity and the sample sizes used to calculate these estimates. For example, you might wish to estimate the prevalence where the true value is assumed to be about 0.01 (1%), and you wish to have 95% (0.95) confidence that the true value is within +/- 0.005 (0.5%) of your estimate, with a test that has a sensitivity of 0.9 (90%) and specificity of 0.99 (99%) and where sensitivity and specificity were estimated using sample sizes of 100 and 1000 respectively. You can also input a suggested pool size if desired, and the program will calculate the corresponding number of pools to be tested for that pool size (in addition to predetermined pool sizes). Suggested pool size is ignored if it is zero.

Outputs

The program calculates the number of pools required for the input-scenario for a range of pool sizes and presents the results in tabular and graphical formats. Results where the recommended number of pools is less than 2 are ignored.

Estimated true prevalence:
Desired precision (+/-):
Desired confidence level:
Test Sensitivity:
Test Specificity:
Sample size for test sensitivity:
Sample size for test specificity:
Suggested pool size:

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