http://spssx-discussion.165.s1.nabble.com/contrast-orthogonal-coding-with-unequal-cell-frequencies-tp5733307p5733319.html
First. Let me say that I do not remember ever using the exact, adjusted coefficients to account for Ns.
Second. The resulting coefficients will be different, at least slightly, when the contrasts correlate,
compared to when the correlation is zero -- what you get from exact weights.
When two terms are uncorrelated, the presence of absence of the second one does not affect the size
of the so-called "partial coefficients" of the other. When they are /nearly/ uncorrelated -- which is
what you usually get with the simple coefficients from Gene -- the sizes are not affected, much. This
is almost always "good enough". But if your Ns are grossly different (yours are, "I don't know"), you
should look at the regression with each predictor without the other, to confirm that they aren't affecting
each other by much.
--
Rich Ulrich
From: SPSSX(r) Discussion <[hidden email]> on behalf of Maguin, Eugene <[hidden email]>
Sent: Wednesday, October 19, 2016 9:38 AM
To: [hidden email]
Subject: Re: contrast (orthogonal) coding with unequal cell frequencies
I re-read the contrast coding section in Cohen (1983) who has a detailed work-through of different coding schemes. He says that with equal cell Ns, the correlations among the contrast variables will be 0.0 but will not be 0.0 if cell
Ns are unequal. However, the B (unstandardized coefficient) values are adjusted for the correlations between the contrast variables. The B values (and its standard error) are what you need to know for the significance of the contrast terms. The answer is No,
do not multiply the contrast coefficient values by the corresponding cell N.
Gene Maguin
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