Re: [R-sig-eco] Log transforming zero value data

2009-07-07 Thread Farrar . David
r-sig-ecology-boun...@r-project.org wrote on 06/24/2009 10:25:25 PM: > [image removed] > > Re: [R-sig-eco] Log transforming zero value data > > Nate Upham > > to: > > Ben Bolker > > 06/25/2009 06:39 AM > > Sent by: > > r-sig-ecology-boun

Re: [R-sig-eco] Log transforming zero value data (+ quantile regression)

2009-06-25 Thread Farrar . David
regression. regards, David r-sig-ecology-boun...@r-project.org wrote on 06/24/2009 10:25:25 PM: > [image removed] > > Re: [R-sig-eco] Log transforming zero value data > > Nate Upham > > to: > > Ben Bolker > > 06/25/2009 06:39 AM > > Sent by: > &

Re: [R-sig-eco] Log transforming zero value data

2009-06-24 Thread Nate Upham
pecific impacts of the habitat variable on average densities in Y? Thanks, --Nate Original message >Date: Wed, 24 Jun 2009 21:25:36 -0400 >From: Ben Bolker >Subject: Re: [R-sig-eco] Log transforming zero value data >To: Nate Upham >Cc: "r-sig-ecology@r-project.org

Re: [R-sig-eco] Log transforming zero value data

2009-06-24 Thread Nate Upham
;Date: Wed, 24 Jun 2009 17:13:07 -0400 >From: Ben Bolker >Subject: Re: [R-sig-eco] Log transforming zero value data >To: Nate Upham >Cc: Matthew Landis , "r-sig-ecology@r-project.org" > > If you have percentage abundances (i.e. you can specify the >"denomi

Re: [R-sig-eco] Log transforming zero value data

2009-06-24 Thread Scott
Hi Nate, Here is my 2 cents worth after coming in late to this discussion. The fact that your data are proportions is important as it suggests how the data may vary. Do you have the numerator and denominator used to calculate the proportions? If so then I would suggest that you should be perf

Re: [R-sig-eco] Log transforming zero value data

2009-06-24 Thread Nate Upham
Thanks very much indeed Carsten and Philippe! Lots to consider. I should have specified this before, but the variable with zero values that I would like to log (ln) transform does consist of many small values. The range is between 0.00 and 0.35, since this variable is the percentage abundan

Re: [R-sig-eco] Log transforming zero value data

2009-06-24 Thread Matthew Landis
Many thanks to Carsten, Philippe, and Nate for a very informative and entertaining discussion of something I have always wondered about, having heard suggestions for both approaches. At least now I have a better understanding of the rationale for each! Matt M

Re: [R-sig-eco] Log transforming zero value data

2009-06-24 Thread Carsten Dormann
Dear Philippe, while I don't like to quibble about rules-of-thumb (since they are, as you rightly point out, without foundation in statistical theory), I would like to correct the impression that you gave in your email. Let's take an hypothetical example along the lines you proposed (or at lea

Re: [R-sig-eco] Log transforming zero value data

2009-06-24 Thread Philippe Grosjean
Carsten Dormann wrote: Dear Nate, although I learned from Phillippe's response about the existence of log1p, I don't think I will use it (for reasons below). Thierry's response is true for Poisson data, but not for non-integer values. Still, it points into an important direction: All too ofte

Re: [R-sig-eco] Log transforming zero value data

2009-06-24 Thread Carsten Dormann
Dear Nate, although I learned from Phillippe's response about the existence of log1p, I don't think I will use it (for reasons below). Thierry's response is true for Poisson data, but not for non-integer values. Still, it points into an important direction: All too often zeros emanate from a

Re: [R-sig-eco] Log transforming zero value data

2009-06-24 Thread ONKELINX, Thierry
Verzonden: woensdag 24 juni 2009 2:31 Aan: r-sig-ecology@r-project.org Onderwerp: [R-sig-eco] Log transforming zero value data I have a general stats question for you guys: How does one normally deal with zero (0) values when log transforming data? I would like to log transform (natural log, ln

Re: [R-sig-eco] Log transforming zero value data

2009-06-24 Thread Philippe Grosjean
See ?log1p Best, Philippe Grosjean ..<°}))>< ) ) ) ) ) ( ( ( ( (Prof. Philippe Grosjean ) ) ) ) ) ( ( ( ( (Numerical Ecology of Aquatic Systems ) ) ) ) ) Mons-Hainaut University, Belgium ( ( ( ( ( ...

[R-sig-eco] Log transforming zero value data

2009-06-23 Thread Nate Upham
I have a general stats question for you guys: How does one normally deal with zero (0) values when log transforming data? I would like to log transform (natural log, ln) several response variables for use in quantile regression. But one of my variables includes several zero values. Since ln(