[R] Comparing two pairs of non-normal datasets in R?

[Peter Sebastian Masny]

On Tuesday 08 June 2004 10:43 am, you wrote:
> If I understand you correctly, you have two set of ***paired***
> data, one set from the A population, and one from the C population.
>
> Form the pairwise differences:
>
> 	A.diff <- A1 - A2
> 	C.diff <- C1 - C2

Alas, they are not paired.  A1 and A2 are samples from the same population, 
but of different members.  Also, the number of measurements is different for 
each dataset.

> Boxplots and histograms of A.diff and C.diff will tell you
> (much more than a test ever would) what's ***really*** going on.

The boxplots I have clearly show the difference, but I need a p value to go 
with it.

Here are the boxplots if that helps:
http://www.ps.masny.dk/guests/misc/A1.png
http://www.ps.masny.dk/guests/misc/A2.png
http://www.ps.masny.dk/guests/misc/C1.png
http://www.ps.masny.dk/guests/misc/C2.png

> P.S. BTW --- you say that your data are continuous, but that their
> distributions are ``more like a Poisson''.  The Poisson distribution
> is DISCRETE!!!

Hence the "like".  The data is indeed continuous, but a distribution graph 
increases towards one extreme...

Visually, the results are convincing, but I really need a test of 
significance.



Thank you very much for the help,

Peter