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help for ^prcounts^ - 11Mar2005
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Compute the predicted rate and probabilities for count models
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    ^prcounts^ varname [^if^ exp] [^in^ range] [^, m^ax^(^max^)^ ^p^lot]

Description
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^prcounts^ computes the predicted rate and probabilities of counts from 0
through the specified maximum count based on the last estimates from the
count models ^poisson^, ^nbreg^, ^zip^, ^zinb^. ^prcounts^ optionally generates
variables for the graphical comparison of observed and expected counts
for one model or for competing models.

For each observation ^prcounts^ computes the variables:

    namerate = predicted count or rate
    namepr^k^ = probability of a count of ^k^ for ^k^=0 to max
    namecu^k^ = cumulative probabiliy of a count  <=^k^ for ^k^=0 to max

For zip or zinb models, prcounts also generates:

    namell0 = probability of being in the 'always zero' group

For ztp or ztnb models, prcounts also generates:

    nameCrate = predicted count or rate conditional on y>0
    nameCpr^k^ = probability of a count of ^k^ for ^k^=0 to max conditional
                    on y>0
    nameCcu^k^ = cumulative probabiliy of a count  <=^k^ for ^k^=0 to max
                    conditional on y>0

Options
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^max(^value^)^  The maximum count for which variables are generated.
    value must be an integer between 0 and 99; the default is 9.

^plot^ causes Stata to generate extra variables that are useful for plotting.
    The created variables will have values for the first max+1 rows of the
    data set.

    nameval = value of y
    nameobeq = observed probability of counts = y
    nameoble = cumulative observed probability of counts <= y
    namepreq = predicted probability of counts = y
    nameprle = predicted cumulative probability of counts <= y

For these variables, each observation provides information about the
probabilities of a given count for the entire sample.  In other words, what
an observation consists of for these variables is different than for the rest
of the variables in one's dataset.

Note: the summary statistics computed by ^plot^ are automatically based on
the estimation sample, plus any further restrictions implied by the use of
^if^ or ^in^.

Examples
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 . ^zinb art fem mar kid5 phd ment, inf(fem mar kid5 phd ment)^
 . ^prcounts cnt^
 . ^summarize cnt*^

To graphically compare predicted and observed counts for a model:

 .^ poisson art fem mar kid5 phd ment^
 .^ prcounts pois, max(8) plot^
 .^ graph poispreq poisobeq poisval, c(ll)^

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Authors: J. Scott Long and Jeremy Freese
         www.indiana.edu/~jsl650/spost.htm
         spostsup@@indiana.edu