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

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

Subject |
RE: st: Treat zeros in logarithms |

Date |
Tue, 26 Aug 2008 18:23:16 +0100 |

I concur with the spirit of Austin's posting. That is, although Emmanouil did not attribute the words "acceptable strategy" to me, I would not single out the trick mentioned in that way. The first issue seems to be: Are the observed zeros (a) sampling or observed or non-detects, i.e. to the best of your knowledge or belief they really are, or should be, positive Or (b) structural or essential only, i.e. they really are, or should be, zero. (Every field seems to have its own jargon, but the same distinction recurs.) If a researcher doesn't know it is difficult to advise. If a researcher does know, it is still difficult to advise, but the desirability of various strategies or tactics should surely vary according to whether (a) or (b) holds. I find the implication that there must be a trick that "solves" this problem at odds with the variety of situations in which it occurs. Nick Austin Nichols Emmanouil <e.mentzakis@abdn.ac.uk>: I looked in vain for the claim about your proposed approach being an acceptable strategy. I believe you are referring to point 4(c) of Nick's post, but the quoted sentence in situ reads "But the appeal here is at best one of simplicity or symmetry, does not apply beyond 2, and does not reflect a statistical argument. More generally, the idea is to replace the zeros by half the smallest non-zero measurement, given some convention about resolution of measurement (e.g. to a fixed number of decimal places using agreed units)." and says nothing about replacing zeros by half the smallest non-zero measurement being an acceptable practice for interval regression. I doubt you will find a published reference claiming it is okay, since any such claim is easy to refute (e.g. via simulation). But ln(0) can be specified as a lower bound in this case... read -help intreg- for specifying an interval (-inf,b. On Tue, Aug 26, 2008 at 12:57 PM, Mentzakis, Emmanouil <e.mentzakis@abdn.ac.uk> wrote: > I have an interval regression model and for some cases the lower bound is zero. As I want to take the logarithm of the bounds I run into problems. > > The same issue has come up previously in the list and below is the link of a detailed answer by Nick Cox. > > http://www.stata.com/statalist/archive/2007-02/msg00046.html > > As Nick points out an acceptable strategy is "...to replace the zeros by half the smallest non-zero measurement..." > > I was wondering if anyone could provide any references of published papers that have employed such approach. * * 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: Treat zeros in logarithms***From:*Maarten buis <maartenbuis@yahoo.co.uk>

**RE: st: Treat zeros in logarithms***From:*"Mentzakis, Emmanouil" <e.mentzakis@abdn.ac.uk>

**References**:**st: Treat zeros in logarithms***From:*"Mentzakis, Emmanouil" <e.mentzakis@abdn.ac.uk>

**Re: st: Treat zeros in logarithms***From:*"Austin Nichols" <austinnichols@gmail.com>

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