On Sep 7, 10:42 am, jim4s...@YAHOO.CO.UK (Jim Groeneveld) wrote:

> Well, that is not so difficult. Just look at the median, not the mean (you > do it nonparametric don't you? Though in the output of NPAR1WAY I see means) > values of your effects; are these in the expected direction? If these are > not included in the standard output it must be possible to caugh them up in > some other way. And you know the direction that you expect. But maybe the > PROC could be more clear about this. Yet it is possible to interprete the > output correctly.

Thanks for your help. It seems that there is indeed sufficient information for me to figure out what is being tested, and how to interpret the one-sided tests, if only I examine enough of the output and understand the convoluted way SAS has set this up.

I guess this now morphs into a rant about why can't SAS make these things clearer. The PROC prints a one-sided test result, but never tells us what the alternative hypothesis is that is being tested. They could have programmed the output to say "One-sided test for Ha: mean (feature) > mean (check)" but they didn't do so.

They write in great detail in the documentation how the test statistic z is computed, but nowhere in that write-up do they discuss exactly what hypothesis z is testing. You have to know enough to use other outputs from the procedure to know what hypothesis is being tested, and it may not be the hypothesis you want to test. This is exactly the opposite of statistical theory, where you state the alternative hypothesis and then compute the test. I have this funny little idea in my head that SAS ought to mirror common statistical practices...

PROC NPAR1WAY isn't the only SAS procedure that does not clearly state the hypothesis being tested, in either the output or in the documentation. When it is difficult for an experienced statistician such as myself to figure out what is being tested, imagine how beginners must feel. And it is so unnecessary ... another 5 hours of programming and testing would have made the PROC NPAR1WAY outputs much clearer.

Seems like a letter of complaint to SAS Institute is in order here, complete with examples where this happens in other PROCs. I will get started.

And finally, I have similar issues with MATLAB as well, so I'm not just picking on SAS. They too are guilty of not explaining things well enough so an experienced statistician knows what is going on. At one point, I wrote to The Mathworks complaining about an example in their documentation, which I said was the most incomplete and misleading example I had ever seen in software documentation.

To both SAS and MATLAB, I say that five more hours of their time would have saved me (and many others) ten hours of my time.

-- Paige Miller paige\dot\miller at kodak\dot\com