Juliet, The answer is simple - add the measured value as an independent variable to the regression. There is no need to convert continuous values to categorical values. If there is a circadian rhythm to the hormone secretion (e.g. cortisol) I would try to get values at the same time of day for all study participants. Baring this, perhaps you could adjust both for the hormone concentration and the time of day the sample was obtained. John
John David Sorkin M.D., Ph.D. Chief, Biostatistics and Informatics University of Maryland School of Medicine Division of Gerontology Baltimore VA Medical Center 10 North Greene Street GRECC (BT/18/GR) Baltimore, MD 21201-1524 (Phone) 410-605-7119 (Fax) 410-605-7913 (Please call phone number above prior to faxing) >>> Juliet Hannah <juliet.han...@gmail.com> 3/7/2009 12:49 PM >>> Hi, This is not an R question, but I've seen opinions given on non R topics, so I wanted to give it a try. :) How would one treat a variable that was measured once, but is known to fluctuate a lot? For example, I want to include a hormone in my regression as an explanatory variable. However, this hormone varies in its levels throughout a day. Nevertheless, its levels differ substantially between individuals so that there is information there to use. One simple thing to try would be to form categories, but I assume there are better ways to handle this. Has anyone worked with such data, or could anyone suggest some keywords that may be helpful in searching for this topic. Thanks for your input. Regards, Juliet ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Confidentiality Statement: This email message, including any attachments, is for th...{{dropped:6}} ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
