Re: contrast (orthogonal) coding with unequal cell frequencies

Posted by Ryan on Oct 21, 2016; 4:00pm
URL: http://spssx-discussion.165.s1.nabble.com/contrast-orthogonal-coding-with-unequal-cell-frequencies-tp5733307p5733353.html

I'd just note that these types of contrasts can easily be accomplished using the TEST statement in MIXED.

Ryan

On Thu, Oct 20, 2016 at 10:48 AM, Bruce Weaver <[hidden email]> wrote:

I haven't had time to follow this thread closely, but perhaps this note by
Dave Howell is relevant?

http://www.uvm.edu/~dhowell/methods7/Errata/Unequal_n's_contrasts.html




Maguin, Eugene wrote
> Rich, I need some education about what you're saying in your reply. That
> first sentence and the phrase "using the Ns". How does using the Ns change
> the construction of the contrast coefficients? To be specific suppose cell
> Ns of 75, 40, 15 and the two contrasts being (-2, 1, 1) and (0, -1, 1).
> Thanks, Gene Maguin
>
>
>
>
>
>
> From: SPSSX(r) Discussion [mailto:

> SPSSX-L@.UGA

> ] On Behalf Of Rich Ulrich
> Sent: Thursday, October 20, 2016 1:24 AM
> To:

> SPSSX-L@.UGA

> Subject: Re: contrast (orthogonal) coding with unequal cell frequencies
>
>
> The big virtue of /orthogonal/ coding, using the Ns, is that the two
> contrasts are created as uncorrelated: which makes
>
> them "unconfounded".  If you use that version, then the coefficients are
> exactly the same whether you look at one
>
> contrast or both; the t-test will vary only to the extent that taking into
> account another variable will reduce the (denominator)
>
> error term.
>
>
>
> As I just posted, with unequal Ns, you can check to see if the simple
> contrasts (not using Ns) do give essentially the same outcome.
>
> If not, then you either look at them together or discuss the mutual impact
> or switch to the other contrasts.
>
>
>
> --
>
> Rich Ulrich
>
> ________________________________
> From: SPSSX(r) Discussion <

> SPSSX-L@.UGA

> <mailto:

> SPSSX-L@.UGA

> >> on behalf of Sidra <

> sidrarashid85@

> <mailto:

> sidrarashid85@

> >>
> Sent: Wednesday, October 19, 2016 10:29 PM
> To:

> SPSSX-L@.UGA

> <mailto:

> SPSSX-L@.UGA

> >
> Subject: Re: contrast (orthogonal) coding with unequal cell frequencies
>
> Note: To be more precise, what I want ask is whether I can treat new
> contrast
> coded variables as individual variables (to represent marital status and
> childbearing status)? or I have to treat them essentialiy as a pair for
> any
> analysis?
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-----
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