Dear R-sig-ecology, I have spent some time trawling the internet, and seem to come across slight conflicting advice regarding the standardisation and transformation of variables prior to multiple regression analysis (e.g. LM, LME/GLS, GLM, GLMM, GAM, GAMM). I searched the archives here and I don't think this is a repeat, but I apologise if it is.
1. I understand that standardisation (subtract mean and divide by standard deviation) is important within a Bayesian environment and when using programs such as Rjags. However within frequentist packages (e.g. lme4, MASS etc) under what (if any) circumstances is it necessary? 2. Are transformations (e.g. log, sqrt etc) necessary for non-normal (highly skewed) explanatory variables or where extreme/outliers are observed. Some literature says this is necessary, other say it is not. Is the current consensus that transformations are generally not required on predictor/explanatory variables? Thank you Sam ________________________________ [http://www.plymouth.ac.uk/images/email_footer.gif]<http://www.plymouth.ac.uk/worldclass> This email and any files with it are confidential and intended solely for the use of the recipient to whom it is addressed. If you are not the intended recipient then copying, distribution or other use of the information contained is strictly prohibited and you should not rely on it. If you have received this email in error please let the sender know immediately and delete it from your system(s). Internet emails are not necessarily secure. While we take every care, Plymouth University accepts no responsibility for viruses and it is your responsibility to scan emails and their attachments. Plymouth University does not accept responsibility for any changes made after it was sent. Nothing in this email or its attachments constitutes an order for goods or services unless accompanied by an official order form. [[alternative HTML version deleted]] _______________________________________________ R-sig-ecology mailing list R-sig-ecology@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-ecology
