Re: REPEATED MIXED MODELS-post hoc tests/contrasts

Posted by Ryan on Jan 10, 2015; 4:16am
URL: http://spssx-discussion.165.s1.nabble.com/REPEATED-MIXED-MODELS-post-hoc-tests-contrasts-tp5728007p5728403.html

I have not been paying close attention to this thread but I happened to read this post and thought I would add to what Gene mentioned. If the model includes a continuous IV ("x1"), categorical IV consisting of two groups ("x2"), and the interaction (x1*x2), then it typically makes sense to determine the shared range of both groups on x1, and estimate the mean difference on the DV between groups at various points across the shared range of x1 such as x1(1st quartile of shared range), x1(median of shared range), and x1(3rd quartile of shared range). 

By estimating the mean difference on the DV between groups at x1 values outside of the shared range, one is extrapolating beyond one or both groups, even if those values are possible. I tend to visualize cliffs as the lower (min value of the shared range) and upper (max value of the shared range) limits of the shared range and as I get closer to either cliff, the certainty of the estimated mean differences on the DV decreases, and beyond the cliffs is uncharted and potentially dangerous territory.

HTH.

Ryan 

On Jan 9, 2015, at 5:20 PM, Maguin, Eugene <[hidden email]> wrote:

Is a score of 17 a valid score for your anxiety measure?  I assumed you had averaged items and your items had a seven point response format. Thus scores would range between 1 and 7. Go back to the plot you made and mark in the possible anxiety score range. If 17 is inside of that range then an interaction makes sense. But suppose that the anxiety score range was 3 to 15. The highest score anybody could receive was 15. Would it make sense to talk about an interaction that required a person to get a score of 17 or more?
Gene Maguin

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From: SPSSX(r) Discussion [[hidden email]] on behalf of Alexandra [[hidden email]]
Sent: Tuesday, January 06, 2015 3:46 PM
To: [hidden email]
Subject: Re: REPEATED MIXED MODELS-post hoc tests/contrasts

Hello,
For LL1-LL3 the interaction is sign for anx score above 17, and for
LL2-LL3 above 24. I don‘t think I get it why, based on your example
with anx ranging Sent from my iPhone
look further :D
The only code that achieves convergence is the one with only the
random intercept and without repeated list length or list length
slope. I'll stick with this then...
For the Johnson Neyman procedure I'll read more from the sources you
recommended. Thanks a lot!

On 12/31/14, Maguin, Eugene [via SPSSX Discussion]
<[hidden email]> wrote:

>
>
> Replies embedded.
>
> From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of
> Alexandra
> Sent: Tuesday, December 30, 2014 1:06 PM
> To: [hidden email]
> Subject: Re: REPEATED MIXED MODELS-post hoc tests/contrasts
>
> As you said, indeed the correlations between LSRT and anxiety in LL1 and LL2
> are very similar, hence the plot shows almost parallel lines for these two
> list lengths. Only for LL3 the slope has a upward direction intersecting the
> regression lines for both LL2 and LL1.
>
> You also said this:
>  "I also want to acknowledge that I am unsure of whether there are
>

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