JSM 2005 Online Program

Abstract #304181

This is the preliminary program for the 2005 Joint Statistical Meetings in Minneapolis, Minnesota. Currently included in this program is the "technical" program, schedule of invited, topic contributed, regular contributed and poster sessions; Continuing Education courses (August 7-10, 2005); and Committee and Business Meetings. This on-line program will be updated frequently to reflect the most current revisions.

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Activity Number:	107
Type:	Contributed
Date/Time:	Monday, August 8, 2005 : 8:30 AM to 10:20 AM
Sponsor:	Section on Statistics and the Environment
Abstract - #304181
Title:	Using Log-ratio-log Plots To Assess the Association between Chemical Species in Environmental Samples
Author(s):	Michael Ginevan*+
Companies:	Exponent, Inc.
Address:	307 Hamilton Avenue, Silver Spring, MD, 20901,
Keywords:	chemical concentration ; graphical display ; constant ratio
Abstract:	Whether a pair of chemical species shows a consistent ratio across a set of environmental samples is a question that often arises because, if the species show constant relative concentration, one may infer the chemical contamination has a common origin. If one had a set of samples that include measurements for both lead (L) and cadmium (C), one might ask if the ratio C/L is consistent across samples. One solution for this problem is to regress ln(C) against ln(L). If this regression fits the data well and the slope is not significantly different from one, one has evidence that the ratio of C/L is constant across samples. However, one may have regressions where fit is good but the slope of the log-log relationship differs from unity. Here, log-log plots of concentration data appear to indicate a consistent relationship where one does not really exist. A better approach is to plot the log of the ratio of the two components against the log of one member of the pair (e.g., ln(C/L) versus ln(L)).

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