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?
Many thanks.
[[alternative HTML version deleted]]