RE : Re: Log transformation of negative values in SAS??
Hi Sami If you are not able to transform yor data so as to notmalise the residuals, you better go fr analytical tools that do not require data to be normally distributed - I guess it will be fine to use non-parametric tests in that case. You will find them easily in SAS... or any other software you have access to.. Hope this is helpful, Robert William Silvert <[EMAIL PROTECTED]> a écrit : Data which are both positive and negative cannot be log transformed. Keep in mind that the purpose of transformation is to normalise the residuals, not to linearise the data. If you cannot find a transformation that normalises the residuals then there are techniques for dealing with the data, although whether you will find a black box to do this in SAS I don't know. Bill Silvert - Original Message - From: "Sami Ullah" To: Sent: Tuesday, January 30, 2007 9:39 PM Subject: Log transformation of negative values in SAS?? > Hello Ecologers: > > I have a data set of N2O fluxes from forest soils in which some values are > positive and some negative. As the distribution in non-normal, I want to > log-transform the data. However, the log transformation command in SAS > transform positive values and ignores the negative. Can anyone guide me on > how to log-transform the data using SAS or anyother software to be able to > take care of both the positive and negative values. > > Thanks in anticipation. > > Sami Ullah > Department of Geography > McGill University, Canada > [EMAIL PROTECTED] > - Découvrez une nouvelle façon d'obtenir des réponses à toutes vos questions ! Profitez des connaissances, des opinions et des expériences des internautes sur Yahoo! Questions/Réponses.
Re: Log transformation of negative values in SAS??
Data which are both positive and negative cannot be log transformed. Keep in mind that the purpose of transformation is to normalise the residuals, not to linearise the data. If you cannot find a transformation that normalises the residuals then there are techniques for dealing with the data, although whether you will find a black box to do this in SAS I don't know. Bill Silvert - Original Message - From: "Sami Ullah" <[EMAIL PROTECTED]> To: Sent: Tuesday, January 30, 2007 9:39 PM Subject: Log transformation of negative values in SAS?? > Hello Ecologers: > > I have a data set of N2O fluxes from forest soils in which some values are > positive and some negative. As the distribution in non-normal, I want to > log-transform the data. However, the log transformation command in SAS > transform positive values and ignores the negative. Can anyone guide me on > how to log-transform the data using SAS or anyother software to be able to > take care of both the positive and negative values. > > Thanks in anticipation. > > Sami Ullah > Department of Geography > McGill University, Canada > [EMAIL PROTECTED] > >
Re: Log transformation of negative values in SAS??
Sami, Remember, depending on the analysis, you want to have normal RESIDUALS and not necessarily normal distributions of the raw data. It is quite possible that you have a normal distribution of your residuals. If not, since you have flux, you could always use the true value for N20 at each measurement, and not flux. The true value will always be positive. Cheers, Jim On 1/30/07, Sami Ullah <[EMAIL PROTECTED]> wrote: > > Hello Ecologers: > > I have a data set of N2O fluxes from forest soils in which some values ar= e > positive and some negative. As the distribution in non-normal, I want to > log-transform the data. However, the log transformation command in SAS > transform positive values and ignores the negative. Can anyone guide me o= n > how to log-transform the data using SAS or anyother software to be able t= o > take care of both the positive and negative values. > > Thanks in anticipation. > > Sami Ullah > Department of Geography > McGill University, Canada > [EMAIL PROTECTED] > --=20 James J. Roper Depto Zoologia,UFPR Caixa Postal 19034 81531-990 Curitiba, Paran=E1, Brasil =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D E-mail: [EMAIL PROTECTED] Phone/Fone/Tel=E9fono:55 41 33611764 celular: 55 41 99870543 Casa: 55 41 33857249 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D http://jjroper.googlepages.com/ Ecologia e Conserva=E7=E3o na UFPR http://www.bio.ufpr.br/ecologia/ ---
Log transformation of negative values in SAS??
Hello Ecologers: I have a data set of N2O fluxes from forest soils in which some values are positive and some negative. As the distribution in non-normal, I want to log-transform the data. However, the log transformation command in SAS transform positive values and ignores the negative. Can anyone guide me on how to log-transform the data using SAS or anyother software to be able to take care of both the positive and negative values. Thanks in anticipation. Sami Ullah Department of Geography McGill University, Canada [EMAIL PROTECTED]
