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| From | "springathens@gmail.com" <springathens@gmail.com> |
| To | statalist@hsphsun2.harvard.edu |
| Subject | Re: st: RE: Checking Goodness of Fit after Zero-inflated Poisson |
| Date | Sun, 22 May 2011 15:04:18 -0400 |
I got it. So, Log likelihood and its corresponding chi-squared already tell the goodness-of-fit. Thanks for your clarification. Sangyub On Sun, May 22, 2011 at 2:56 PM, Nick Cox <n.j.cox@durham.ac.uk> wrote: > You shouldn't need to ask. Your question was already answered in my post. > > As the example output shows, -zip- already shows a LR chi-square statistic and a P-value. > > Nick > n.j.cox@durham.ac.uk > > springathens@gmail.com > > Thanks Nick for your response. > > First, sorry for not understanding the name policy. I will sincerely > follow the rules. > > Ok, after I run a standard Poisson, I can compute the goodness-of-fit > by using the command -estat gof-. For instance, after I run Poisson, > -estat gof- reports as follows: > > . poisson day windcat du50 du100 du150 > > Iteration 0: log likelihood = -186.58213 > Iteration 1: log likelihood = -183.38329 > Iteration 2: log likelihood = -183.34036 > Iteration 3: log likelihood = -183.34036 > > Poisson regression Number of obs = 125 > LR chi2(4) = 606.33 > Prob > chi2 = 0.0000 > Log likelihood = -183.34036 Pseudo R2 = 0.6231 > > ------------------------------------------------------------------------------ > day | Coef. Std. Err. z P>|z| [95% Conf. Interval] > -------------+---------------------------------------------------------------- > windcat | .6731493 .0625124 10.77 0.000 .5506273 .7956713 > du50 | 2.550244 .3132588 8.14 0.000 1.936268 3.16422 > du100 | 2.144695 .3203497 6.69 0.000 1.516821 2.772568 > du150 | 2.07342 .3292282 6.30 0.000 1.428144 2.718695 > _cons | -2.008924 .2934786 -6.85 0.000 -2.584132 -1.433716 > ------------------------------------------------------------------------------ > > . estat gof > > Goodness-of-fit chi2 = 118.6753 > Prob > chi2(120) = 0.5170 > > But, that command does not work after zip. How may I compute the > goodnes-of-fit? Or, does zip already report the goodness-of-fit in its > result table? > > Hope this clarifies my question. > > Thanks again, > Sangyub Ryu > > On Sun, May 22, 2011 at 2:18 PM, Nick Cox <n.j.cox@durham.ac.uk> wrote: >> Dear Spring [in?] Athens: >> >> Please note the request in the Statalist FAQ to use real names. >> >> From a -zip- I see output like this >> >> Zero-inflated Poisson regression Number of obs = 250 >> Nonzero obs = 108 >> Zero obs = 142 >> >> Inflation model = logit LR chi2(2) = 506.48 >> Log likelihood = -850.7014 Prob > chi2 = 0.0000 >> >> ------------------------------------------------------------------------------ >> count | Coef. Std. Err. z P>|z| [95% Conf. Interval] >> -------------+---------------------------------------------------------------- >> count | >> persons | .8068853 .0453288 17.80 0.000 .7180424 .8957281 >> livebait | 1.757289 .2446082 7.18 0.000 1.277866 2.236713 >> _cons | -2.178472 .2860289 -7.62 0.000 -2.739078 -1.617865 >> -------------+---------------------------------------------------------------- >> inflate | >> child | 1.602571 .2797719 5.73 0.000 1.054228 2.150913 >> camper | -1.015698 .365259 -2.78 0.005 -1.731593 -.2998038 >> _cons | -.4922872 .3114562 -1.58 0.114 -1.10273 .1181558 >> ------------------------------------------------------------------------------ >> >> What else, precisely, do you have in mind by "goodness of fit"? >> >> Nick >> n.j.cox@durham.ac.uk >> >> springathens@gmail.com >> >> I am using zero-inflated Poisson regression. >> Unlike a standard Poisson regression, neither -estat gof- nor >> -poisgof- commands report the goodness of fit for a zero-inflated >> Poisson. >> How may I find the goodness of fit for zero-inflated Poisson regression? > > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/