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 5^{th} percentile of 0.75 (75%), and the second is for a distribution with a mode at 0.75 and the 95^{th} 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: