mom: Method of Moments

In wrbrignon/BrignonPackage: Functions that I use regularly

Description

Method of Moments to determine parameters for gamma or beta distributions.

Usage

mom(distribution, mean, sd)

Arguments

distribution	enter "beta" or "gamma"
mean	mean value of samples
sd	standard deviation of samples

Value

Returns parameters a (i.e., shape 1) and b (i.e., shape 2) of the beta distribution.

Returns parameters c (i.e., shape) and b (i.e., rate) of the gamma distribution. Note that the scale parameter = 1/b (See example).

A warning will show if negative values are obtained. distribution.

Examples

##Beta Distribution
##assign beta parms from mean = 0.5 and sd = 0.2 to outz
outz = mom("beta",0.5, 0.2)

##use outz to generate 10 random beta observations from mean = 0.5 and sd = 0.2
rbeta(10,outz[1],outz[2])

##Example of negative parameter estimate function
mom("beta",50, 0.2)

##Gamma Distribution
##Generate some probability levels
prob_levels<-c(0.001,.05,.25,.5,.75,.95,0.999)

##Generate gamma parms with man of 10 and sd of 5
outz <- mom("gamma",10, 5)

##Use the gamma parms (outz) and the probability with qgamma to find the
##quantile values of a gamma dist. Note the 1/b component to calculate the scale parameter
qgamma(prob_levels,outz[1],1/outz[2])

wrbrignon/BrignonPackage documentation built on May 4, 2019, 10:54 a.m.