mom: Method of Moments

Description Usage Arguments Value Examples

View source: R/Method of moments.R

Description

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

Usage

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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

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##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.