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Re: category.c
From: |
Jason Stover |
Subject: |
Re: category.c |
Date: |
Tue, 21 Mar 2006 16:05:48 -0500 |
User-agent: |
Mutt/1.5.10i |
On Tue, Mar 21, 2006 at 08:35:52AM +0800, John Darrington wrote:
> 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.
Yeah. And I don't think the warning is necessary. (I was thinking users
should enter a '0' or '1' but make the type categorical, but that doesn't
happen, and often shouldn't happen, as in the case where 'average sex is
.54' just means '54% female.')
-Jason