# interpreting one-way anova tables

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## interpreting one-way anova tables

 Hi, I am trying to reconcile anova table in R (summary(lm)) with individual t.test. datafilename="http://personality-project.org/R/datasets/R.appendix1.data" data.ex1=read.table(datafilename,header=T)   #read the data into a table summary(lm(Alertness~Dosage,data=data.ex1)) gives: Call: lm(formula = Alertness ~ Dosage, data = data.ex1) Residuals: Â Â  MinÂ Â Â Â  1Q MedianÂ Â Â Â  3QÂ Â Â  Max -8.500 -2.437Â  0.250Â  2.687Â  8.500 Coefficients: Â Â Â Â Â Â Â Â Â Â Â  Estimate Std. Error t value Pr(>|t|)Â Â Â  (Intercept)Â Â  32.500Â Â Â Â Â  2.010Â  16.166 6.72e-11 *** DosagebÂ Â Â Â Â Â  -4.250Â Â Â Â Â  2.659Â  -1.598 0.130880Â Â Â  DosagecÂ Â Â Â Â  -13.250Â Â Â Â Â  3.179Â  -4.168 0.000824 *** --- Signif. codes:Â  0 â***â 0.001 â**â 0.01 â*â 0.05 â.â 0.1 â â 1 Residual standard error: 4.924 on 15 degrees of freedom Multiple R-squared: 0.5396,Â Â Â Â  Adjusted R-squared: 0.4782 F-statistic: 8.789 on 2 and 15 DF,Â  p-value: 0.002977 As far as I understand it the lines "Dosageb" and "DosageC" represent the difference between DosageA and the other two dosages. My question is this: are these differences and the p-values associated with them the same as a t.test or pairwise.t.test on these groups? If I do t.tests, I get different values for t and p-value from those in the anova table above. Can someone please explain what the discrepancy is? Thanks               [[alternative HTML version deleted]] ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.