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

[Lutz Prechelt]

> 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

Here is how I would do it:
It looks like your distributions can be characterized by
just a single parameter.

Then your question is:
   Is the change in the parameter value from A1 to A2
   larger than that from C1 to C2?
(Larger meaning what?: Difference? Ratio?)

So I suggest
- you estimate your four parameters
- compute your two differences or ratios
- compute the difference of those
- and repeat all this for many resamples (bootstrapping)

Then you get a bootstrap distribution of the 
value that you hope is significantly non-zero.
>From that distribution you can read your p-value.
(Preferably based on a BCa confidence interval)

library(boot)

Does that make sense?

  Lutz