[R] How to test for the difference of means in population, please help

[Greg Snow]

You should use mixed effects modeling to analyze data of this sort.
This is not a topic that has generally been covered by introductory
classes, so you should consult with a professional statistician on
your problem, or educate yourself well beyond the novice level (this
takes more than just reading 1 book, a few classes would be good to
get to this level, or intense study of several books).

Since everything is balanced nicely, you could average over the 4
repeats and use a 2 sample t test (assuming the assumptions hold, your
sample data would be fine) comparing the 2 sets of 400 means.  This
will test for a general difference in the overall means, but ignores
other information and hypotheses that may be important (which is why
the mixed effects model approach is much preferred).

On Tue, Mar 27, 2012 at 1:13 AM, ali_protocol
<mohammadianalimohammadian at gmail.com> wrote:
> Dear all,
>
> Novice in statistics.
>
> I have 2 experimental conditions. Each condition has ~400 points as its
> response. Each condition is done in 4 repereats (so I have 2 x 400 x 4
> points).
>
> I want to compare the means of two conditions and test whether they are same
> or not. Which test should I use?
>
> #populations
> c = matrix (sample (1:20,1600, replace= TRUE), 400 ,4)
> b = matrix (sample (1:20,1600, replace= TRUE), 400 ,4)
>
> #means of repeats
> c.mean= apply (c,2, mean)
> b.mean= apply (b,2,mean)
>
> #mean of experiment
> c.mean.all= mean (c)
> b.mean.all= mean (b)
>
> --
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> Sent from the R help mailing list archive at Nabble.com.
>
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-- 
Gregory (Greg) L. Snow Ph.D.
538280 at gmail.com