Analyzing frequencies in R
Dear Manuel, You can use the Wilson method (with Yates' continuity correction) to calculate CIs for proportion data. It's formally described and advocated in the following articles: Newcombe R.G. (1998) Two-Sided Confidence Intervals for the Single Proportion: Comparison of Seven Methods. Statistics in Medicine 17, 857?872. Newcombe R.G. (1998) Interval Estimation for the Difference Between Independent Proportions: Comparison of Eleven Methods. Statistics in Medicine 17, 873?890. In R, it's implemented in prop.test (which also allows two-sample testing of equal proportions). Cheers, Phil
At 08:13 AM 6/8/2009, Manuel Sp?nola wrote:
Dear list members, If I have 3 frequencies (3 mutually exclusive groups): white: 19 black: 43 red: 24 How can I obtain confidence intervals for the proportions, instead of a P value from a chisquare test in R? Or better, how can I assess "effect size" instead of finishing the analysis on a P value when analyzing frequencies in R? Is it possible to obtain standardized Pearson residuals in this situation? Thank you very much in advance. Best, Manuel Sp?nola -- Manuel Sp?nola, Ph.D. Instituto Internacional en Conservaci?n y Manejo de Vida Silvestre Universidad Nacional Apartado 1350-3000 Heredia COSTA RICA mspinola at una.ac.cr mspinola10 at gamil.com Tel?fono: (506) 2277-3598 Fax: (506) 2237-7036
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Phil Novack-Gottshall pnovackg at westga.edu Assistant Professor Department of Geosciences University of West Georgia Carrollton, GA 30118-3100 Phone: 678-839-4061 Fax: 678-839-4071 http://www.westga.edu/~pnovackg ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~