Hi, I am encountering a difficulty I don't understand. Be patient, I'm very
new to analysis of variance.
If I load this data:
example12_7=read.table("http://msemac.redwoods.edu/~darnold/math15/data/chapter12/example12_7.dat",header=TRUE)
The run the oneway.test:
oneway.test(time~drug,data=example12_7,var.equal=TRUE)
I get these results:
data: time and drug
F = 4.1881, num df = 2, denom df = 16, p-value = 0.03445
Now, I've done the problem by hand and this result agrees with my
calculations. Now I try aov and get these results:
res1 <- aov(time~drug,data=example12_7)
summary(res1)
Df Sum Sq Mean Sq F value Pr(>F)
drug 1 7.96 7.964 2.417 0.138
Residuals 17 56.01 3.294
Note these do not agree with above. However, if I enter the data by hand:
Drug1=c(7.3,8.2,10.1,6.0,9.5)
Drug2=c(7.1,10.6,11.2,9.0,8.5,10.9,7.8)
Drug3=c(5.8,6.5,8.8,4.9,7.9,8.5,5.2)
boxplot(Drug1,Drug2,Drug3)
Then create a dataframe:
d=stack(list(Drug1=Drug1,Drug2=Drug2,Drug3=Drug3))
And run aov again:
res=aov(values~ind,data=d)
summary(res)
I get these results:
Df Sum Sq Mean Sq F value Pr(>F)
ind 2 21.98 10.991 4.188 0.0345 *
Residuals 16 41.99 2.624
Which completely agree with my calculations. What's going on?
Thanks.
D.
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