Hi Emma, ...
I forgot to add the tabular ouput, which doesn't help either: T.sum <- summary(aov(response ~ group, data=TDat)) print(T.sum) Df Sum Sq Mean Sq F value Pr(>F) group 1 11225.2 11225.2 3084 < 2.2e-16 *** Residuals 198 720.7 3.6 --- Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 unlist(T.sum) unlist(T.sum)[5]/unlist(T.sum)[6] Mean Sq1 3084.028 Regards, Mark. Mark Difford wrote: > > Hi Emma, > >>> ...from this I can read the within-group variance. can anyone tell me >>> how i may find >>> out the between-group variance? > > But it's in the table, above the "within-group" variance. Remember that F > is the ratio of these two quantities, i.e. the mean of the group variances > divided by the mean of the within-group variances . I will work with my > example since you never set seed so your answers are different from mine > (which really does not help matters). > > set.seed(7) > TDat <- data.frame(response = c(rnorm(100, 5, 2), rnorm(100, 20, 2))) > TDat$group <- gl(2, 100, labels=c("A","B")) > summary(aov(response ~ group, data=TDat)) > > 11225.25/3.64 > [1] 3083.86 > > There is some rounding error on the mean squares (i.e. mean variances) but > F is correct. Using estimates calculated by a different route we have: > > 11225.249057/3.639801 > [1] 3084.028 > > Does this answer your question? > > Regards, Mark. > > > emj83 wrote: >> >> I have done this in R and this is the following ANOVA table I get: >> >>> summary(aov(response ~ group, data=TDat)) >> Df Sum Sq Mean Sq F value Pr(>F) >> group 1 11203.5 11203.5 2505.0 < 2.2e-16 *** >> Residuals 198 885.5 4.5 >> >> The model is response(i,j)= group(i)+ error(i,j), >> >> we assume that group~N(0,P^2) and error~N(0,sigma^2) >> >> I know that sigma^2 is equal to 4.5, how do I find out P^2? >> >> In the problem that I am trying to apply this to, I have more than 2 >> groups. I was hoping there would be a function that helps you do this >> that I don't know about. >> >> >> Thanks for your help Emma >> >> >> >> >> Mark Difford wrote: >>> >>> Hi Emma, >>> >>>>> >>> >>> R gives you the tools to work this out. >>> >>> ## Example >>> set.seed(7) >>> TDat <- data.frame(response = c(rnorm(100, 5, 2), rnorm(100, 20, 2))) >>> TDat$group <- gl(2, 100, labels=c("A","B")) >>> with(TDat, boxplot(split(response, group))) >>> summary(aov(response ~ group, data=TDat)) >>> >>> Regards, Mark. >>> >>> >>> emj83 wrote: >>>> >>>> can anyone advise me please? >>>> >>>> >>>> emj83 wrote: >>>>> >>>>> I have done some ANOVA tables for some data that I have, from this I >>>>> can read the within-group variance. can anyone tell me how i may find >>>>> out the between-group variance? >>>>> >>>>> Thanks Emma >>>>> >>>> >>>> >>> >>> >> >> > > -- View this message in context: http://www.nabble.com/Between-group-variance-from-ANOVA-tp24954045p25130266.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.