> Yes, it is possible to lose your mind on this (so perhaps get a real name). > A good friend here is > > ?dummy.coef
When I use it, it complained: > dummy.coef(yy) Error in dd$A1 : $ operator is invalid for atomic vectors What's wrong? > > In your case (i.e. treatment contrasts), your reference level for the > interaction terms are the reference levels of the factors themselves. In > your example, these seem to be A1 and b1. Assuming they are, the coefficient > for, say, dd$AA3:dd$Bb2 is worked out relative to them. > dd$AA3:dd$Bb2 is relative to dd$AA1 only, or dd$Bb1 only , or dd$AA1 + dd$Bb1, or dd$AA1 : dd$Bb1, or dd$AA1 * dd$Bb1 That's exactly where I was not sure about! >> Call: >> lm(formula = dd$Y~ dd$A * dd$B) >> >> Residuals: >> Min 1Q Median 3Q Max >> -1.68582 -0.42469 -0.02536 0.20012 3.50798 >> >> Coefficients: >> Estimate Std. Error t value Pr(>|t|) >> (Intercept) 4.40842 0.40295 10.940 5.34e-13 *** >> dd$AA2 0.11575 0.56986 0.203 0.8402 >> dd$AA3 0.01312 0.56986 0.023 0.9818 >> dd$AA4 -0.06675 0.56986 -0.117 0.9074 >> dd$AA5 0.10635 0.56986 0.187 0.8530 >> dd$AA6 0.11507 0.56986 0.202 0.8411 >> dd$Bb2 -0.58881 0.56986 -1.033 0.3084 >> c 0.26465 0.80590 0.328 0.7445 >> dd$AA3:dd$Bb2 0.40984 0.80590 0.509 0.6142 >> dd$AA4:dd$Bb2 -0.02918 0.80590 -0.036 0.9713 >> dd$AA5:dd$Bb2 0.35574 0.80590 0.441 0.6616 >> dd$AA6:dd$Bb2 1.55424 0.80590 1.929 0.0617 . >> --- >> Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 >> >> Residual standard error: 0.8059 on 36 degrees of freedom >> Multiple R-squared: 0.2642, Adjusted R-squared: 0.03934 >> F-statistic: 1.175 on 11 and 36 DF, p-value: 0.3378 >> >> ______________________________________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide >> http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code. >> >> > > -- > View this message in context: > http://www.nabble.com/question-about-contrast-in-R-for-multi-factor-linear-regression-models--tp20413510p20416877.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
