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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
RE: st: RE: Fractional Logit |

Date |
Sun, 30 Oct 2005 21:54:41 -0000 |

You misunderstand my previous posts. I was at some pains to emphasise that it is almost impossible, at least for me, to specify what is appropriate for your case on the information you provide. I did not "recommend" -betafit-. Clive Nicholas mentioned -mlbeta-. I just pointed out that -betafit- is in the same territory. More important, the -alpha()- and -beta()- options of -betafit- are explained in its help file. Again, the appropriate ways to include arguments for these options would presumably be some combination of theory and inspection of the data... Nick n.j.cox@durham.ac.uk Rijo John > Thanking you for all your suggestions. Since my dependent variable is > certainly a proportion between 0 and 1 (and not a binary with only 0,1 > values) now I am faced with three options. > > 1) fractional logit model as in glm command (Where I am still not sure > which family link combination to be used) > 2) mlbeta as suggested by clive > 3) betafit as suggested by Nick > > Nick, could you please explain the portion "alphavar(varlist1) > betavar(varlist2)" in betafit command? Is there any standard way of > deciding which are the variables to be included in the varlist1 and > varlist2 for alphavar and betavar respectively? > On Sun, 30 Oct 2005, Nick Cox wrote: > > <If that is a possibility, so also is the -betafit- > <of Stephen Jenkins et alius, downloadable from SSC. > < > <Nick > <n.j.cox@durham.ac.uk > < > <Clive Nicholas > < > <> Rijo John replied to Nick Cox: > <> > <> > Thanks Nick. I am trying to estimate the impact of spending on a > <> > particular commodity (say X) on the purchase of other goods > <> and services. > <> > So I have the share of, say commodity Y (Its share in > <> household budget) > <> > as the dependent variable and the expenditure on > commodity X along > <> with > <> > various control variables for household as explanatory > <> variables. This > <> > can be a standrad OLS estimation. But since the depended > <> variable is a > <> > fraction and is bound between 0 and 1 we go for fractional > <> logit model. > <> > > <> > I hope this clarifies the problem. Given this I would like > <> to know what > <> > would be the right choice of family and link in GLM. > <> > > <> > "family(gaussian) link(logit)" or "family(binomial) > <> link(logit)" or some > <> > other combination? > <> > > <> > in "family(binomial) link(logit)" is it tru that stata > <> takes all values > <> > other than 0 in the dependent variable as 1. If thats the > <> case it does > <> > not take the budget share (absolute amount) information > <> into account. It > <> > will only see if the budget share is absent or not. > <> > <> Since your dependent variable is a fractional, or 'compositional', > <> variable ranging continuously from 0 to 1, another > <> alternative is to use > <> Sean 'Jack' Buckley's -mlbeta-. This allows maximum > <> likelihood estimation > <> with Beta-distributed dependent variables, as well as > <> modelling separate > <> equations for both a mean and dispersion effect. This > routine is _not_ > <> downloadable from SSC, so type: > <> > <> . net from http://www2.bc.edu/~bucklesj > <> > <> and then click on -mlbeta-. Hope that helps. * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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