Notice: On March 31, it was **announced** that Statalist is moving from an email list to a **forum**. The old list will shut down on April 23, and its replacement, **statalist.org** is already up and running.

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

From |
Nick Cox <njcoxstata@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Model for Poisson-shaped distribution but with non-count data |

Date |
Wed, 7 Dec 2011 09:13:52 +0000 |

-lnskew0- is a transformation command rather than a modelling command. Its use would, in my view, create two key problems even if it "worked". 1. You still have to explain to whoever you are writing for why using ln(y - k) (in the most common case) makes scientific sense. Of course, you may have a rationale for that. The usual rationale is that this is in effect fitting a three-parameter lognormal distribution and there is some clearcut reason why there is a definite lower limit to values and also that it needs to be estimated from the data. Conversely if you know k as a fixed minimum, there is no need to estimate it. No covariates appear in this story. 2, The estimation of k and the estimation of whatever parameters you use in any subsequent modelling command (in which covariates are now introduced) are uncoupled, which is at best statistically awkward. If you feed the results of -lnskew0- to a modelling command, you are neglecting the uncertainty about k. In short, I would never use -lnskew0- unless it was _exactly_ what I wanted. Nick On Tue, Dec 6, 2011 at 8:48 PM, Owen Gallupe <ogallupe@gmail.com> wrote: > Thank you for the input, Cam, Paul, Paul, Nick, David, and Bill. > > You have given me some very good options to consider. > > Regarding Cam's earlier question, the multimodality only surfaces when > the DV is transformed using lnskew0. It is not an issue using the raw > version. > * * 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/

**Follow-Ups**:**Re: st: Model for Poisson-shaped distribution but with non-count data***From:*Owen Gallupe <ogallupe@gmail.com>

**References**:**Re: st: Model for Poisson-shaped distribution but with non-count data***From:*"William Gould, StataCorp LP" <wgould@stata.com>

**Re: st: Model for Poisson-shaped distribution but with non-count data***From:*Owen Gallupe <ogallupe@gmail.com>

- Prev by Date:
**Re: st: Question on graph twoway and graph combine** - Next by Date:
**Re: st: Question on graph twoway and graph combine** - Previous by thread:
**RE: st: Model for Poisson-shaped distribution but with non-count data** - Next by thread:
**Re: st: Model for Poisson-shaped distribution but with non-count data** - Index(es):