Silk Purse Spreadsheet

R. H. Zander

Res Botanical Web Site

Missouri Botanical Garden

March 24, 2005

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This MS Excel spreadsheet allows calculation of confidence intervals for each composite internode created from several internodes on a cladogram with less than fully reliable confidence intervals.


The chance of at least one of two or more chained internodes being correct is calculable with a simple probability formula, namely one minus (the product of the chances each internode is incorrect), where the chance of being incorrect is 1 minus the CL (or BPP). This is the Formula for Implied Reliability.


In addition, a spreadsheet calculation for Bayes’ Formula is given. One may produce a posterior probability for a branch arrangement by using as a prior a previous result for that branch arrangement. For morphological results, assign an arbitrary 0.95 prior if the branch arrangement agrees with molecular result, 0.05 if disagrees, 0.50 if equivocal or contested.  Note that previously published branch arrangements less than 0.50 probability must be included to avoid simply choosing probabilities greater than 0.50, which will always increase the posterior probability.


This spreadsheet supports various papers submitted for publication, see my reprint URLs.


For more information, contact author Richard Zander


To download the spreadsheet, click here.