# gammaGetShapeRate: Convert gamma mean and dispersion parameters to shape and... In kgoldfeld/simstudy: Simulation of Study Data

## Description

Convert gamma mean and dispersion parameters to shape and rate parameters

## Usage

 `1` ```gammaGetShapeRate(mean, dispersion) ```

## Arguments

 `mean` The mean of a gamma distribution `dispersion` The dispersion parameter of a gamma distribution

## Details

In simstudy, users specify the gamma distribution as a function of two parameters - a mean and dispersion. In this case, the variance of the specified distribution is (mean^2)*dispersion. The base R function rgamma uses the shape and rate parameters to specify the gamma distribution. This function converts the mean and dispersion into the shape and rate.

## Value

A list that includes the shape and rate parameters of the gamma distribution

## Examples

 ```1 2 3 4 5 6 7 8``` ```set.seed(12345) mean = 5; dispersion = 1.5 rs <- gammaGetShapeRate(mean, dispersion) c(rs\$shape, rs\$rate) vec <- rgamma(1000, shape = rs\$shape, rate = rs\$rate) (estMoments <- c(mean(vec), var(vec))) (theoryMoments <- c(mean, mean^2*dispersion)) (theoryMoments <- c(rs\$shape/rs\$rate, rs\$shape/rs\$rate^2)) ```

kgoldfeld/simstudy documentation built on Dec. 23, 2018, 5:33 a.m.