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Confidence
interval calculation for source partitioning using stable isotopes
ISOERROR1_04 is a Microsoft Excel 2000™ spreadsheet which calculates estimates and confidence intervals of source proportional contributions to a mixture, using stable isotope analyses. Examples include the proportions of different food sources in an animal’s diet, C3 vs. C4 plant inputs to soil organic carbon, etc. Linear mixing models are used to partition two sources with a single isotopic signature (e.g., d13C) or three sources with a second isotopic signature (e.g., d15N). See Phillips and Gregg (2001), Uncertainty in source partitioning using stable isotopes, Oecologia 127: 171-179, for further details about the calculations. PDF files for the published paper (Phillips & Gregg.pdf) and corrections for errors the publisher introduced into the equations (published erratum.pdf) are given below. PDF files can be read and printed using Adobe Acrobat Reader™, which is available for downloading free of charge at www.adobe.com
The user supplies the mean, standard deviation, and number of samples from each of the source and mixture populations for each isotope. For dual isotope studies, the correlations of the two isotopes within each population can also be specified, but are not required. The spreadsheet calculates the estimate proportion for each source (0-1), standard errors for these estimates, and approximate 95% confidence intervals. Confidence intervals are truncated at 0 and 1.
This software is provided free of charge with the
understanding that it will not be used for any commercial purposes. It is
reasonably reliable, but has not been exhaustively tested and must be applied
at the user's own risk. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
Several minor changes have been made since the previous versions of this
spreadsheet. Please use only the latest version (1_04) below.
isoerror1_04.xls [Excel 2000™ spreadsheet]
Phillips & Gregg.pdf [published paper]
published erratum.pdf [equation corrections]
To obtain further information, contact Don Phillips
Accesses since April 20, 2006..