# Re: st: how to use ztnb?

 From nicola.baldini2@unibo.it To statalist@hsphsun2.harvard.edu Subject Re: st: how to use ztnb? Date Fri, 22 Feb 2008 18:57:29 +0100

```Which is the question, here? Your knowledge of -ztnb- seems to exceed mine. Your code
xi:ztnb mf-counts i.age [fweight = freq] if mf-counts>0, dispersion(mean)
let you estimate a zero truncated NB mobel where the dispersion (the parameter called dispersion in Stata) is a nonlinear (exponential) function of the mean. As a default, it includes a test about the hypothesis that the dispersion is a nonlinear (exponential) function of the mean vs. the dispersion is a constant (if the test is insignificant, then the dispersion is a constant).
Nicola

At 02.33 19/02/2008 -0500, Subramanian Swaminathan wrote:
>Dear stata listers,
>
>I am trying to fit a zero-truncated negative binomial
>model to my count
>data. The data variables are mf-counts, age,
>frequency. The model that I
>would like to fit is of the form:
>xi:ztnb mf-counts i.age [fweight = freq] if
>mf-counts>0, dispersion(mean)
>
>Kindly note that my dispersion parameter is not a
>constant but is a
>non-linear function as given below:
>
>k = k0+beta*mean**gamma (0<gamma < infinity)
>
>where,
>'k' is the dispersion parameter 'k' ( in stata, k=log
>(1/alpha) of the
>negative bonomial model
>
>beta & gamma = coefficients to be estimated
>
>In this model I want to test the hypothesis that
>beta=0 against beta not
>equal to 0.
>
>could anyone help me out, how the stata code should be
>written to estimate
>the parameters of the model?
>
>kindly note that i am new stata.

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