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Re: category.c
From: |
John Darrington |
Subject: |
Re: category.c |
Date: |
Tue, 21 Mar 2006 08:35:52 +0800 |
User-agent: |
Mutt/1.5.9i |
On Mon, Mar 20, 2006 at 10:03:27AM -0500, Jason Stover wrote:
> 3. cat_value_update seems to do nothing for numeric variables. Why is
> this? A numeric variable can be used as a categorical variable
> just as easily as an alpha one.
Good point. Encoding numeric data as categorical is usually a mistake
from a statistical standpoint, but there are circumstances when
treating a numeric variable as categorical makes perfect sense, so
maybe cat_value_update() shouldn't care what type of variable it is
looking at. This is where the question 'should we protect the user?'
comes up. Someone with a numeric variable that has, say, 10^5 distinct
values and inadvertently treats that variable as categorical could
wind up running a procedure with 0 or negative degrees of freedom;
slowing the machine down to a crawl; or, worst of all, finding bugs
we'd rather not know about. But users should probably have the ability
to treat numeric data as categorical if they want to.
I'm not a statistician, so I can't make any comment about whether
numeric variables, "ought" to be used as catagorical ones. But I've
seen *many* examples where this is done. Most demonstrations of
T-TEST do something like 0 = Male, 1 = Female. I've even seen reports
telling me that a person's average sex is 0.54 Maybe we could have a
very mild warning if a catagorical variable is numeric.
While we're on the topic, is anyone in favor of using a garbage
collector in PSPP?
Using pool.c sort of does something similar. Perhaps we should make
more use of that.
J'
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