Simple 2-Way Anova issue in R
If I've understood correctly, you have cell sizes of 1. This is not enough. ANOVA compares within group variance to between group variance, and your within group variances are zero. You need more data, or to collapse some cells. Jeremy 2009/11/8 znd <zackdaugherty at mail.com>:
Hello, I'm new to R and have been following many guides including the two-way anova (http://www.personality-project.org/r/r.anova.html). ?Using that walkthrough including the supplied data I do str(data.ex2) and receive the appropriate types of data as follows:
str(data.ex2)
'data.frame': ? 16 obs. of ?4 variables: ?$ Observation: int ?1 2 3 4 5 6 7 8 9 10 ... ?$ Gender ? ? : Factor w/ 2 levels "f","m": 2 2 2 2 2 2 2 2 1 1 ... ?$ Dosage ? ? : Factor w/ 2 levels "a","b": 1 1 1 1 2 2 2 2 1 1 ... ?$ Alertness ?: int ?8 12 13 12 6 7 23 14 15 12 ... aov.ex2 = aov(Alertness~Gender*Dosage,data=data.ex2) summary(aov.ex2) Outputs: ? ? ? ? ? ? ?Df ?Sum Sq Mean Sq F value Pr(>F) Gender ? ? ? ? 1 ?76.562 ?76.562 ?2.9518 0.1115 Dosage ? ? ? ? 1 ? 5.062 ? 5.062 ?0.1952 0.6665 Gender:Dosage ?1 ? 0.063 ? 0.063 ?0.0024 0.9617 Residuals ? ? 12 311.250 ?25.938 However, when I got to use my data that I made in csv format I have to tell R to interpret my factors which are year and depth as factors... datafilename="C:/Rclass/hmwk1pt2.csv" data.ex2=read.csv(datafilename,header=T) data.ex2$Year<-as.factor(data.ex2$Year) data.ex2$Depth<-as.factor(data.ex2$Depth) data.ex2 str(data.ex2) This outputs what I would expect:
str(data.ex2)
'data.frame': ? 12 obs. of ?4 variables: ?$ Year ? ? ?: Factor w/ 3 levels "1999","2000",..: 1 1 1 1 2 2 2 2 3 3 ... ?$ Depth ? ? : Factor w/ 4 levels "10","15","20",..: 1 2 3 4 1 2 3 4 1 2 ... ?$ Replicate1: num ?14.3 15.1 16.7 17.3 16.3 17.4 18.6 20.9 22.9 23.9 ... ?$ Replicate2: num ?14.7 15.6 16.9 17.9 16.4 17.2 19.6 21.3 22.7 23.3 ... But something is not causing my anova to carry through...this is what I have. ANOVA = aov(Replicate1~Year*Depth,data=data.ex2) summary(ANOVA) which outputs:
summary(ANOVA)
? ? ? ? ? ?Df ?Sum Sq Mean Sq Year ? ? ? ? 2 143.607 ?71.803 Depth ? ? ? ?3 ?17.323 ? 5.774 Year:Depth ? 6 ? 2.587 ? 0.431 There is no F-value or Pr(>F) columns. I also can't boxplot this correctly, again following the example at that website above they have: boxplot(Alertness~Dosage*Gender,data=data.ex2) which outputs: http://old.nabble.com/file/p26258684/87o3uicpf6dt4kkdyvfv.jpeg My code is: boxplot(Replicate1~Year*Depth,data=data.ex2) which outputs: http://old.nabble.com/file/p26258684/gik02vyhvvbmcvw3ia2h.jpeg This is incorrect, it's multiplying my factors but I thought that when I did the str() on my data it recognized the Year and Depth as factors, not numbers or integers. My csv file is: http://old.nabble.com/file/p26258684/hmwk1pt2.csv hmwk1pt2.csv Any help on what is going one would be greatly appreciated because I need to perform one-way, two-way, nested, and factorial anovas but I first need to solve this problem before I can continue. -- View this message in context: http://old.nabble.com/Simple-2-Way-Anova-issue-in-R-tp26258684p26258684.html Sent from the R help mailing list archive at Nabble.com.
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Jeremy Miles Psychology Research Methods Wiki: www.researchmethodsinpsychology.com