On May 11, 2013, at 06:10 , meng wrote: > Hi all: > > I have a question about one-way anova. > > The data is ¡°sleep¡±which belongs to R. > > > > code1: > > summary(lm(extra~group)) > > > > Estimate of group2(1.58) is the difference between mean of group1 and > group2,and t value(1.861) and p value(0.0792) is the same as 2 sample t > test,and the code is ¡° t.test(extra~group)¡±. > > > > My question: > > The p value of Intercept(0.2276) tests for what? > > > > My guess is test the difference between mean of group1 vs 0: > > dat1<-extra[group==1] > > t.test(dat1,mu=0) > > > > But the p value is 0.2176,which is different from 0.2276 of lm result. > > > > > > > > code2: > > summary(lm(extra~group+0)) > > > > The pvalue of group1(0.2276) and group2(0.0011). > > > > My question: > > The p value of group1 and group2 tests for what? > > > > My guess is test the difference between mean of group1 vs 0 and group2 vs 0: > > > > dat1<-extra[group==1] > > t.test(dat1,mu=0) > > > > The p value is 0.2176,which is different from 0.2276 of lm result. > > > > dat2<-extra[group==2] > > t.test(dat2,mu=0) > > > > The p value is 0.005076, which is different from 0.0011 of lm result. > > > > > > So,what¡¯s wrong with my guess? >
You need to pay more attention to the degrees of freedom for error. -- Peter Dalgaard, Professor, Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Email: pd....@cbs.dk Priv: pda...@gmail.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.
