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Article #3594data transformation theory...
From: Evan Cooch
Date: Fri, 31 Jan 1992 20:20
Date: Fri, 31 Jan 1992 20:20
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2153 bytes
In a somewhat-related following question to my recent posting concerning code
for Box-Cox transformations, recent discussions with some statistical types
suggests that the following might be of general interest.
Suppose you want to do a simple analysis, say a single-classification
anova. There are 5 levels of the classification variable. You do
whatever homogeneity of variance/normality tests you subscribe to, and you
find that the data is either/or heteroscedastic or non-normal.
However, you also notice that no SINGLE transformation can be applied to
all groups. I.E maybe x^2 works for data in one group, while log(x)
works for another. Alternatively, the "best" Box-Cox transform differes
among groups.
Question: If you can't use the same transform for all your data, should
you transform at all?
Funny how all the intro biometry texts talk about transformations, but none
of them that I've seen address this.
_///_ +----------------------------+
-. .- | Evan G. Cooch |
( L ) \//// | Department of Biology |
--(\=/)-- ( ) | University of Pennsylvania |
/ \ / / | Philadelphia, Pennsylvania |
I V / | Phone: (215) 898-7129 |
I / | FAX: (215) 898-8780 |
I / | ECOOCH@PENNSAS.UPENN.EDU |
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X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f5efb,9a8189043869e961,start X-Google-Attributes: gidf5efb,public X-Google-ArrivalTime: 1992-01-31 14:43:49 PST Comments: Gated by NETNEWS@AUVM.AMERICAN.EDU Path: arc1-ca.pugleaf.net!sparky!uunet!wupost!psuvax1!psuvm!auvm!PENNSAS.UPENN.EDU!ECOOCH Message-ID: <STAT-L%92013115292678@VM1.MCGILL.CA> Newsgroups: bit.listserv.stat-l Date: Fri, 31 Jan 1992 15:20:08 EST Sender: "STATISTICAL CONSULTING" <STAT-L@MCGILL1.BITNET> From: Evan Cooch <ECOOCH@PENNSAS.UPENN.EDU> Subject: data transformation theory... X-To: STAT-L@MCGILL1.BITNET, SAS-L@OHSTVMA.BITNET