help cdfplot
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Title

  Plots the cumulative distribution function

Syntax

        cdfplot varname [if] [in] [weight] [, options]

    options               Description
    -------------------------------------------------------------------------
    Main
      by(varname)          specifies a separate c.d.f. to be drawn for each
                            value of varname.
      normal               specifies that a Gaussian probability curve with
                            the same mean and standard deviation to be
                            superimposed over the c.d.f.
      samesd               specifies that the normal c.d.f.s use the same
                            same standard deviation.
      nocdf                specifies that the empirical c.d.f. is not drawn.
      opt1(twoway_options)
                            specifies the additional graph options for the
                            c.d.f. plot.
      opt2(twoway_options)
                            specifies the additional graph options for the
                            Gaussian c.d.f. plots .
      twoway_options       any twoway options are applied to the final graph.
    -------------------------------------------------------------------------


Description

    cdfplot plots the sample cumulative distribution function. Distributions
    can be compared within subgroups defined by a second variable. The best
    fitting normal (Gaussian) model may be superimposed over the sample
    c.d.f.

Updating this command using SSC

    To obtain the latest version click the following to uninstall the old
    version

    ssc uninstall cdfplot

    And click here to install the new version

    ssc install cdfplot

Options

    by(varname) specifies a separate c.d.f. to be drawn for each value of
        varname. These are plotted on the same graph for easier comparison.

    normal specifies that a normal probability curve with the same mean and
        standard deviation to be superimposed over the c.d.f.

    samesd is relevant only when by and normal options are used together.  It
        specifies that the normal curves with different means have the same
        standard deviations.  This demonstrates the fit of the conventional
        Gaussian location shift model.

    nocdf specifies that the empirical c.d.f. is not drawn but this option
        will not work unless the normal option is specified, hence only the
        smoothed Gaussian c.d.f will be drawn.

    opt1(twoway_options) specifies additional graph options for the c.d.f.
        plots.

    opt2(twoway_options) specifies additional graph options for the Gaussian
        c.d.f. plots.

    If the xlog option is used, the normal option causes log-normal
        distributions to be fitted.

Examples

    Using the variable length from the auto data (click on the following
    commands in order):

    NOTE DATA will be lost when loading new data

    sysuse auto,replace
    cdfplot length, normal
    cdfplot length, by(foreign)
    cdfplot length, by(foreign) norm saving(mygraph)
    cdfplot length [fw=rep78], by(foreign) norm saving(mygraph,replace)

    Using the variable bp from the bplong data

    sysuse bplong,replace
    cdfplot bp, norm
    cdfplot bp, by(agegrp)
    cdfplot bp, by(agegrp) norm

    Now to show the use of the options in the individual graphs, opt1 alters
    the line colours for the c.d.f. graphs and opt2 alters the line pattern
    for the Gaussian c.d.f.

    cdfplot bp, by(agegrp) opt1( lc(red green olive) ) opt2( lp(dash dash
    dash) ) norm

Author

    Adrian Mander, MRC Human Nutrition Research Unit, Cambridge, UK.

    Email adrian.mander@mrc-hnr.cam.ac.uk


Acknowledgement

    This command is nearly a direct port of the cdf command that was written
    by David Clayton and Michael Hills in STB-49.

Also see

    cdf (if installed)