20 Multicomp - Multiple Comparisons Reference: Steel and...

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Multiple Comparisons Reference: Steel and Torrie, 1980, Principles and Procedures of Statistics, McGraw/Hill
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Red clover: Trifolium pratense { Vermont state flower http://www.50states.com/flower/vermont.htm
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Rhizobium trifolii Appl Environ Microbiol. 1984 December; 48(6): 1140–1150.
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{ Nitrogen content in milligrams was measured on red clover plants inoculated with cultures of Rhizobium trifolii plus a composite of five R. meliloti strains. http://www.fcps.k12.va.us/StratfordLandingES/Ecology/mpages/red_clover.htm Does Rhizobium strain influence the nitrogen content of clover?
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Reading nitrogen data into Splus/R nitrogen = data.frame( strain = c( rep("k1",5), rep("k5",5), rep("k4",5), rep("k7",5), rep("k13",5), rep("com",5)), N.content = c(19.4,32.6,27.0,32.1,33.0, 17.7,24.8,27.9,25.2,24.3, 17.0,19.4, 9.1,11.9,15.8, 20.7,21.0,20.5,18.8,18.6, 14.3,14.4,11.8,11.6,14.2, 17.3,19.4,19.1,16.9,20.8))
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Formatting data for output data.frame( split(nitrogen$N.content, nitrogen$strain)) com k1 k13 k4 k5 k7 1 17.3 19.4 14.3 17.0 17.7 20.7 2 19.4 32.6 14.4 19.4 24.8 21.0 3 19.1 27.0 11.8 9.1 27.9 20.5 4 16.9 32.1 11.6 11.9 25.2 18.8 5 20.8 33.0 14.2 15.8 24.3 18.6
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Formatting data for output data.frame( split(nitrogen$N.content, nitrogen$strain)) [,c(2,4,5,6,3,1)] k1 k4 k5 k7 k13 com 1 19.4 17.0 17.7 20.7 14.3 17.3 2 32.6 19.4 24.8 21.0 14.4 19.4 3 27.0 9.1 27.9 20.5 11.8 19.1 4 32.1 11.9 25.2 18.8 11.6 16.9 5 33.0 15.8 24.3 18.6 14.2 20.8
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10 15 20 25 30 com k1 k13 k4 k5 k7 Nitrogen (mg) Nitrogen Content (mg) by Strain
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Nitrogen means and standard error k13 k4 com k7 k5 k1 Nitro Mean 13.26 14.64 18.70 19.92 23.98 28.82 Nitro SE 0.64 1.84 0.72 0.51 1.69 2.59
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nitrogen.aov = aov(N.content~strain,data=nitrogen) summary(nitrogen.aov) Df Sum of Sq Mean Sq F Value Pr(F) strain 5 847.04 169.41 14.37 0.000 Residuals 24 282.93 11.79 The ANOVA indicates a statistically significant difference, but is that enough?
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( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) com-k1 com-k13 com-k4 com-k5 com-k7 k1-k13 k1-k4 k1-k5 k1-k7 k13-k4 k13-k5 k13-k7 k4-k5 k4-k7 k5-k7 -20 -15 -10 -5 0 5 10 15 20 25 simultaneous 95 % confidence limits, Tukey method response variable: N.content Multiple Comparisons!
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multicomp(nitrogen.aov)
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This note was uploaded on 11/29/2010 for the course STSCI 3010 at Cornell University (Engineering School).

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20 Multicomp - Multiple Comparisons Reference: Steel and...

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