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01-21-2012 04:10 AM

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01-23-2012 07:34 AM

Some more info about the X and Y variables would be a lot of help. Looking at the plot that accompanied your post, I didn't see much but noise. The X variable looks to get very large, so a plot of Y vs. log(X) might be revealing. I don't think there is going to be anything, but you might look at PROC TRANSREG for Box-Cox transformations as a step towards something.

Steve Denham

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01-23-2012 08:29 AM

If the X axis is reversed, this looks like a classic case of heteroskedastic data in which the variance increases with X.

I'd define Z = 1/X and plot Y vs. Z (or use 1/(X+1) if X=0 is a possible value).

You can then use all the standard variance stabilizing transformations (AKA, normalizing transformations) such as Z-->log(Z) or Z-->sqrt(Z).

Depending on the meaning of X, you could also try just a simple reflection such as W = 300000 - x and then work with W.

As Steve mentions, transformations often work best when they are meaningfully related to the data. So ask yourself, is "natural" way to flip around the X axis?