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79 lines
2.7 KiB
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79 lines
2.7 KiB
Plaintext
.-
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help for ^prcounts^ - 11Mar2005
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.-
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Compute the predicted rate and probabilities for count models
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-------------------------------------------------------------
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^prcounts^ varname [^if^ exp] [^in^ range] [^, m^ax^(^max^)^ ^p^lot]
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Description
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-----------
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^prcounts^ computes the predicted rate and probabilities of counts from 0
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through the specified maximum count based on the last estimates from the
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count models ^poisson^, ^nbreg^, ^zip^, ^zinb^. ^prcounts^ optionally generates
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variables for the graphical comparison of observed and expected counts
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for one model or for competing models.
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For each observation ^prcounts^ computes the variables:
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namerate = predicted count or rate
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namepr^k^ = probability of a count of ^k^ for ^k^=0 to max
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namecu^k^ = cumulative probabiliy of a count <=^k^ for ^k^=0 to max
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For zip or zinb models, prcounts also generates:
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namell0 = probability of being in the 'always zero' group
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For ztp or ztnb models, prcounts also generates:
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nameCrate = predicted count or rate conditional on y>0
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nameCpr^k^ = probability of a count of ^k^ for ^k^=0 to max conditional
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on y>0
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nameCcu^k^ = cumulative probabiliy of a count <=^k^ for ^k^=0 to max
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conditional on y>0
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Options
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-------
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^max(^value^)^ The maximum count for which variables are generated.
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value must be an integer between 0 and 99; the default is 9.
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^plot^ causes Stata to generate extra variables that are useful for plotting.
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The created variables will have values for the first max+1 rows of the
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data set.
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nameval = value of y
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nameobeq = observed probability of counts = y
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nameoble = cumulative observed probability of counts <= y
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namepreq = predicted probability of counts = y
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nameprle = predicted cumulative probability of counts <= y
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For these variables, each observation provides information about the
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probabilities of a given count for the entire sample. In other words, what
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an observation consists of for these variables is different than for the rest
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of the variables in one's dataset.
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Note: the summary statistics computed by ^plot^ are automatically based on
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the estimation sample, plus any further restrictions implied by the use of
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^if^ or ^in^.
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Examples
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--------
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. ^zinb art fem mar kid5 phd ment, inf(fem mar kid5 phd ment)^
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. ^prcounts cnt^
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. ^summarize cnt*^
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To graphically compare predicted and observed counts for a model:
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.^ poisson art fem mar kid5 phd ment^
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.^ prcounts pois, max(8) plot^
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.^ graph poispreq poisobeq poisval, c(ll)^
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.-
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Authors: J. Scott Long and Jeremy Freese
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www.indiana.edu/~jsl650/spost.htm
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spostsup@@indiana.edu
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