eqlogis {EnvStats}  R Documentation 
Estimate Quantiles of a Logistic Distribution
Description
Estimate quantiles of a logistic distribution.
Usage
eqlogis(x, p = 0.5, method = "mle", digits = 0)
Arguments
x 
a numeric vector of observations, or an object resulting from a call to an
estimating function that assumes a logistic distribution
(e.g., 
p 
numeric vector of probabilities for which quantiles will be estimated.
All values of 
method 
character string specifying the method to use to estimate the distribution parameters.
Possible values are

digits 
an integer indicating the number of decimal places to round to when printing out
the value of 
Details
The function eqlogis
returns estimated quantiles as well as
estimates of the location and scale parameters.
Quantiles are estimated by 1) estimating the location and scale parameters by
calling elogis
, and then 2) calling the function
qlogis
and using the estimated values for
location and scale.
Value
If x
is a numeric vector, eqlogis
returns a
list of class "estimate"
containing the estimated quantile(s) and other
information. See estimate.object
for details.
If x
is the result of calling an estimation function, eqlogis
returns a list whose class is the same as x
. The list
contains the same components as x
, as well as components called
quantiles
and quantile.method
.
Note
The logistic distribution is defined on the real line and is unimodal and symmetric about its location parameter (the mean). It has longer tails than a normal (Gaussian) distribution. It is used to model growth curves and bioassay data.
Author(s)
Steven P. Millard (EnvStats@ProbStatInfo.com)
References
Forbes, C., M. Evans, N. Hastings, and B. Peacock. (2011). Statistical Distributions. Fourth Edition. John Wiley and Sons, Hoboken, NJ.
Johnson, N. L., S. Kotz, and N. Balakrishnan. (1995). Continuous Univariate Distributions, Volume 2. Second Edition. John Wiley and Sons, New York.
See Also
elogis
, Logistic, estimate.object
.
Examples
# Generate 20 observations from a logistic distribution with
# parameters location=0 and scale=1, then estimate the parameters
# and estimate the 90th percentile.
# (Note: the call to set.seed simply allows you to reproduce this example.)
set.seed(250)
dat < rlogis(20)
eqlogis(dat, p = 0.9)
#Results of Distribution Parameter Estimation
#
#
#Assumed Distribution: Logistic
#
#Estimated Parameter(s): location = 0.2181845
# scale = 0.8152793
#
#Estimation Method: mle
#
#Estimated Quantile(s): 90'th %ile = 1.573167
#
#Quantile Estimation Method: Quantile(s) Based on
# mle Estimators
#
#Data: dat
#
#Sample Size: 20
#
# Clean up
rm(dat)