LISTSERV at the University of Georgia
Menubar Imagemap
Home Browse Manage Request Manuals Register
Previous messageNext messagePrevious in topicNext in topicPrevious by same authorNext by same authorPrevious page (February 2005)Back to main SPSSX-L pageJoin or leave SPSSX-L (or change settings)ReplyPost a new messageSearchProportional fontNon-proportional font
Date:         Thu, 3 Feb 2005 17:10:59 +0100
Reply-To:     Marta García-Granero
              <biostatistics@terra.es>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Marta García-Granero
              <biostatistics@terra.es>
Organization: Asesoría Bioestadística
Subject:      Re: Confidence intervals for geometric mean
In-Reply-To:  <OF847F5196.D7D93153-ON85256F9D.004D11EC-85256F9D.004D510A@hivresearch.org>
Content-Type: text/plain; charset=ISO-8859-15

Hi Christian,

Working with GM is the same as working with the arithmetic mean of the log(data). Compute CI for the mean of log(data), then take the antilog of the limits.

I don't know of any nonparametric test that compares GM. If the log(data) are roughtly normal, then run a t test on them and antilog the limits of the CI for mean diferences (be careful with the interpretation of the antilog results, you will get CI for the ratio of both GM).

Take a look at these on-line articles (from British Medical Journal):

Transforming data: http://bmj.bmjjournals.com/cgi/content/full/312/7033/770

Transformations, means and confidence intervals: http://bmj.bmjjournals.com/cgi/content/full/312/7038/1079

The use of transformation when comparing two means: http://bmj.bmjjournals.com/cgi/content/full/312/7039/1153

CB> I am looking some script to estimate the confidence intervals at 95% for CB> geometric mean (GM) values. In addition, I have two groups and I am CB> thinking to apply a non-parametric test to compare their GMs.If you have CB> others ways to compare GM, please go ahead, welcome all ideas and comments.

HTH Marta mailto:biostatistics@terra.es


Back to: Top of message | Previous page | Main SPSSX-L page