Date: Sun, 25 Sep 2005 13:03:01 +0200
Reply-To: Marta García-Granero
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: Marta García-Granero
Organization: Asesoría Bioestadística
Subject: Re: MANCOVA data transformation
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JH> I am analyzing the data for my dissertation and I've got a Box's M on one
JH> of my DV's (I can tell which one, due to outliers on each end). Since the
JH> DV is a ratio, arcsine has been suggested to me as a transformation.
Are you talking about a percentage or just the ratio of two
Arcsin transformation is suitable for percentages (or fractions, but not
any ratio) that are likely to follow a binomial law (instead of the
normal law), provided that the denominator is a constant. If lack of
HOV is caused simply by some outliers, but not because your data are
binomially distributed, then it is not a good idea at all to arcsin
JH> do you think would be best? And can I only transform one of the two DV's,
JH> or do I have to do both? Also, once I transform the data, what other
JH> things do I need to keep in mind when looking at other parts of the data?
JH> Meaning, the means of the DV etc. These have to be converted back, yes?
Some transformations can be undone, that's why I consider a bit
dangerous to use then without a solid reason.