[R] ANOVA
Kingsford Jones
kingsfordjones at gmail.com
Fri Mar 6 00:42:27 CET 2009
On Thu, Mar 5, 2009 at 8:31 AM, kayj <kjaja27 at yahoo.com> wrote:
>
> Hi All,
>
>
> I have about one hundred patients and all the patients had their glucose
> measured on three different days. The days are all the same for all he
> patients. So I have three measurement for each patient . I want to know
> whether the day when the glucose was measured has an effect on the
> measurements. I was thinking to use a single factor analysis of variance but
> I am not sure how to do it in R.
Two options for one-way ANOVA are aov(response ~ factor), or
lm(response ~ factor) followed by anova(lm.object).
But....this would probably be a bad idea. I recommend Pinheiro and
Bates (2000), where there are many examples of modeling effects within
subjects over time.
Here's an example with a continuous time effect
library(nlme)
f1 <- lme(distance~age, data=Orthodont, random= ~1 + age|Subject,
weights=varPower())
plot(f1, distance~fitted(.)|Subject, abline=c(0,1))
intervals(f1)
hth,
Kingsford Jones
>any other suggestion on dealing with this
> problem is welcome.
>
> Thanks,
>
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