Dear Pikal, All levels except the interactions are compared to the Intercept. I'm a little confused as to what's going on in interaction terms eg. the cell wool B : tension M. It's mean is : 28.78 and 28.78 - 44.56 = -15.78 != 21.111.
It's something like 44.56 (intercept) -16.333 (wool B) -.20.556 (tension M) + 21.111 (woolB:tensionM) = 28.782. I don't know how to sum up the above line in terms of differences succinctly. Best Regards, Ashim On Fri, Dec 2, 2016 at 5:11 PM, PIKAL Petr <petr.pi...@precheza.cz> wrote: > Hi > > You probably could get better answer from experts but it has something to > do with contrasts. > > ?contrasts > > Number 44.556 is mean for wool A and tension L and this is the level to > which every other level is compared. > > Cheers > Petr > > > -----Original Message----- > > From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of Ashim > > Kapoor > > Sent: Thursday, December 1, 2016 2:48 PM > > To: r-help@r-project.org > > Subject: [R] Interpreting summary.lm for a 2 factor anova > > > > Dear all, > > > > Here is a small example : - > > > > > model <- aov(breaks ~ wool * tension, data = warpbreaks) > > > summary.lm(model) > > > > Call: > > aov(formula = breaks ~ wool * tension, data = warpbreaks) > > > > Residuals: > > Min 1Q Median 3Q Max > > -19.5556 -6.8889 -0.6667 7.1944 25.4444 > > > > Coefficients: > > Estimate Std. Error t value Pr(>|t|) > > (Intercept) 44.556 3.647 12.218 2.43e-16 *** > > woolB -16.333 5.157 -3.167 0.002677 ** > > tensionM -20.556 5.157 -3.986 0.000228 *** > > tensionH -20.000 5.157 -3.878 0.000320 *** > > woolB:tensionM 21.111 7.294 2.895 0.005698 ** > > woolB:tensionH 10.556 7.294 1.447 0.154327 > > --- > > Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 > > > > Residual standard error: 10.94 on 48 degrees of freedom > > Multiple R-squared: 0.3778, Adjusted R-squared: 0.3129 > > F-statistic: 5.828 on 5 and 48 DF, p-value: 0.0002772 > > > > > model.tables(model,"e") > > Tables of effects > > > > wool > > wool > > A B > > 2.8889 -2.8889 > > > > tension > > tension > > L M H > > 8.241 -1.759 -6.481 > > > > wool:tension > > tension > > wool L M H > > A 5.278 -5.278 0.000 > > B -5.278 5.278 0.000 > > > > > > > model.tables(model,"m") > > Tables of means > > Grand mean > > > > 28.14815 > > > > wool > > wool > > A B > > 31.037 25.259 > > > > tension > > tension > > L M H > > 36.39 26.39 21.67 > > > > wool:tension > > tension > > wool L M H > > A 44.56 24.00 24.56 > > B 28.22 28.78 18.78 > > > > > > > I don't follow the output of summary.lm. 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