```Date: Nov 30, 2012 11:09 PM
Author: Ray Koopman
Subject: Re: En passant question: What if a plot of slope CI<br>	’s is lousy, but splits the “m’s” perfectly?

On Nov 30, 7:54 am, djh <halitsk...@att.net> wrote:> Consider the following plot of slope CI?s (paste into fixed font> document if it wraps):>>    ----------m----------> a1,1,C> --------------------m--------------------> b1,1,C>             ---------m---------> c2,1,C>                      -----m-----> b47,1,C>                           -----m----> c1,1,C>                            -----m-----> a3,1,C>                               -----m----> c2,1,S>                               -----m------> c1,1,S>                               ------m-----> a1,1,S>                                     -----m-----> b47,1,S>                                 ----------m----------> a3,1,S>                     ------------------------m------------------------> b1,1,S>> Between ?C? and ?S? slopes, there is obviously no CI split at all.>> But there is a perfect split of ?m?s?.>> Can?t anything be concluded from the perfect split of ?m?s??>> (I think I know what your answer will be but wanted to check> nonetheless.)If all the true slopes were identical and the sampling distributionsof the sample slopes were symmetric then the probability of havingall C < all S, or vice versa, would be 2*6!^2/12! = 1/462 = .0022,so it certainly looks like there's a subset effect. It might be moreto the point to do S vs C t-tests for each fold separately. And, inthe same spirit, for each cell in the Fold x LengthInterval design.(Those are the same heteroscedastic t's you've been doing. Don't give the data to Excel and tell it to do a t-test.)
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