# findbetaqq: The findbetaqq function In PriorGen: Generates Prior Distributions for Proportions

## Description

A function to estimate the parameters alpha and beta of a Beta distribution based on the existing prior belief (data and/or expert opinion) about the values of two distinct percentiles.

## Usage

 `1` ```findbetaqq(percentile.value1,percentile1,percentile.value2,percentile2) ```

## Arguments

 `percentile.value1` specify the value for the first percentile. It takes a value between 0 and 1. `percentile1` specify which is the percentile that corrersponds to percentile.value1. It takes a value between 0 and 1. `percentile.value2` specify the value for the second percentile. It takes a value between 0 and 1. `percentile2` specify which is the percentile that corrersponds to percentile.value2. It takes a value between 0 and 1.

## References

Kostoulas, P., Nielsen, S. S., Branscum, A. J., Johnson, W. O., Dendukuri, N., Dhand, N. K., Toft, N., Gardner, I. A. (2017): Reporting guidelines for diagnostic accuracy studies that use Bayesian latent class models (STARD–BLCM). Statistics in medicine, 23, 3603–3604.

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18``` ```##Example 1 ##We believe that 20% of the units in an area/region have a prevalence of ##disease/infection less than or equal to 0.30 while at the same time we are 90% ##certain that the prevalence is less than 0.60 findbetaqq(percentile.value1=0.30,percentile1=0.20,percentile.value2=0.60,percentile2=0.90) ##The output is: ##[1] "The desired Beta distribution that satisfies the specified conditions is: ##Beta( 5.19 7.17 )" ##[1] "Here is a plot of the specified distribution." ##[1] "Descriptive statistics for this distribution are:" ## Min. 1st Qu. Median Mean 3rd Qu. Max. ##0.02999 0.31999 0.41419 0.41974 0.51413 0.85487 ##[1] "Verification: The first percentile value 0.3 corresponds to the 0.2 th ##percentile" ##[1] "Verification: The second percentile value 0.6 corresponds to the 0.9 th ##percentile" ```

PriorGen documentation built on May 1, 2019, 9:17 p.m.