Pooled Prevalence Calculator – Demonstration analyses

Estimation of alpha and beta Parameters for Prior Beta distributions

This program calculates the alpha and beta parameters for prior Beta distributions used in the Bayesian analyses, based on the values specified for the mode and 5th or 95th percentile of the distribution. The mode and percentiles can be estimated either from existing data or from expert opinion.

For this analysis, two estimates were calculated. The first for a distribution with a mode of 0.9 (90%) and a 5th percentile of 0.75 (75%), and the second is for a distribution with a mode at 0.75 and the 95th percentile at 0.9. input values and results are summarised below:

Distribution

 Mode 

 5/95 percentile 

 Alpha value 

 Beta value 

1

0.9

0.75

22.99

3.44

2

0.75

0.9

7.39

3.13

Density curves for the two distributions are:

and:

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