------------------------------------------------------------------------------- help forpexp-------------------------------------------------------------------------------

Probability plot for data versus fitted exponential distribution

pexpvarname[ifexp] [inrange] [weight] [,gridparam(#)show(condition)generate(newvar1 newvar2)graph_options]where

graph_optionsare

rlopts(cline_options)plot(plot)scatter_optionstwoway_options

fweights,aweights andiweights are allowed; see help weights.

Description

pexpproduces a probability plot forvarnamecompared with a one-parameter exponential distribution with probability density function for variablexof (1/m) exp(-x/m). The parametermis by default calculated as the mean of the data specified.

RemarksIn the majority of cases,

pexpwill be used to fit an exponential distribution on the fly and to assess that fit. In some cases, it may be of interest to compare data with an exponential distribution with a known or hypothesised mean, which may be specified using theparam()option. In all cases it is important not only to specify anyiforinrestrictions, but also to specify relevant weights, which will (unless constant) affect the configuration of the plot.

Options

gridis equivalent toyla(0(.25)1, grid) xla(0(.25)1, grid).

param()may be used to supply a parameter value (namely, the mean) directly for use in estimation of fitted quantiles.

show()may be used to specify that you wish to restrict the graph according to some condition, say looking at one tail of the distribution only. Note thatifandinshould not be used for this purpose.

generate()specifies the names of two new variables, the first to hold exponential probabilities and the second to hold empirical probabilities.

graph_optionsarerlopts(cline_options),plot(plot),scatter_options, andtwoway_options

rlopts(cline_options)affect the rendition of the reference line; see help cline_options.

plot(plot)provides a way to add other plots to the generated graph; see help plot_option.

scatter_optionsaffect the rendition of the plotted points; see help scatter.

twoway_optionsare any of the options documented in help twoway_options excludingby(). These include options for titling the graph (see help title_options) and options for saving the graph to disk (see help saving_option).

Examples

. pexp spacing

. pexp spacing, param(20)

. pexp spacing, gen(spacing_exp spacing_emp)

AuthorNicholas J. Cox, University of Durham, U.K. n.j.cox@durham.ac.uk

Also see