Let's be careful here. aov() treats block as a **random** error component of variance. lm() treats block as a **fixed effect**. That's a different kettle of fish. Perhaps both Kevin and the authors of his textbook need to read up on fixed versus random effects and what they mean -- and what sorts of tests make sense for each.
Bert Gunter Genentech Nonclinical Statistics -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of T.K. Sent: Tuesday, December 04, 2007 2:46 PM To: Zembower, Kevin Cc: r-help@r-project.org Subject: Re: [R] Learning to do randomized block design analysis This seems to work. The trick is to use 'lm' instead of 'aov'. > model.aov <- lm(Score.changes ~ factor(Therapy) + factor(Block), data=table) > anova(model.aov) Analysis of Variance Table Response: Score.changes Df Sum Sq Mean Sq F value Pr(>F) factor(Therapy) 2 260.93 130.47 15.259 0.001861 ** factor(Block) 4 438.00 109.50 12.807 0.001484 ** Residuals 8 68.40 8.55 --- Signif. codes: 0 ?**?0.001 ?*?0.01 ??0.05 ??0.1 ??1 On Dec 4, 2007 12:15 PM, Zembower, Kevin <[EMAIL PROTECTED]> wrote: > We just studied randomized block design analysis in my statistics class, > and I'm trying to learn how to do them in R. I'm trying to duplicate a > case study example from my textbook [1]: > > > # Case Study 13.2.1, page 778 > > cd <- c(8, 11, 9, 16, 24) > > dp <- c(2, 1, 12, 11, 19) > > lm <- c(-2, 0, 6, 2, 11) > > table <- data.frame(Block=LETTERS[1:5], "Score changes"=c(cd, dp, > lm), Therapy=rep(c("Contact Desensitisztion", "Demonstration > Participation", "Live Modeling"), each=5)) > > table > Block Score.changes Therapy > 1 A 8 Contact Desensitisztion > 2 B 11 Contact Desensitisztion > 3 C 9 Contact Desensitisztion > 4 D 16 Contact Desensitisztion > 5 E 24 Contact Desensitisztion > 6 A 2 Demonstration Participation > 7 B 1 Demonstration Participation > 8 C 12 Demonstration Participation > 9 D 11 Demonstration Participation > 10 E 19 Demonstration Participation > 11 A -2 Live Modeling > 12 B 0 Live Modeling > 13 C 6 Live Modeling > 14 D 2 Live Modeling > 15 E 11 Live Modeling > > model.aov <- aov(Score.changes ~ Therapy + Error(Block), data=table) > > summary(model.aov) > > Error: Block > Df Sum Sq Mean Sq F value Pr(>F) > Residuals 4 438.0 109.5 > > Error: Within > Df Sum Sq Mean Sq F value Pr(>F) > Therapy 2 260.93 130.47 15.259 0.001861 ** > Residuals 8 68.40 8.55 > --- > Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 > > > > I don't understand why R doesn't output a value for F and Pr for the > Error (Block) dimension, as my textbook shows 12.807 and 0.0015 > respectively. All the other numbers match. Can these two values be > recovered? Also, my text shows a total line which R omits. Is this > because it's not particularly useful? > > Thanks for your suggestions and advice. Also, if I'm executing this type > of problem in R inefficiently, I'd appreciate suggestions. > > -Kevin > > [1] An Introduction to Mathematical Statistics and Its Applications, > Larsen and Marx, fourth edition. > > Kevin Zembower > Internet Services Group manager > Center for Communication Programs > Bloomberg School of Public Health > Johns Hopkins University > 111 Market Place, Suite 310 > Baltimore, Maryland 21202 > 410-659-6139 > > ______________________________________________ > 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. > -- ====================================== T.K. (Tae-kyun) Kim Ph.D. student Department of Marketing Marshall School of Business University of Southern California ====================================== [[alternative HTML version deleted]] ______________________________________________ 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.
