[R] Comparing two pairs of non-normal datasets in R?
Lutz Prechelt
prechelt at pcpool.mi.fu-berlin.de
Wed Jun 9 17:58:26 CEST 2004
> 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
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