Thanks for your input.
Best,
Greg
On 21/11/2013 5:38 PM, MCLAREN, Donald wrote:
>
> On Thu, Nov 21, 2013 at 11:09 AM, Greg Reckless
> <[log in to unmask] <mailto:[log in to unmask]>> wrote:
>
> Thanks Donald. I avoided including an EV for each of the three
> groups as the wiki suggested this would cause a rank-deficiency with
> the EVs modeling the subject-specific means (which is the error msg
> I get when I add them). Do you have any additional thoughts on
> this, i.e. is this a warning that can be ignored?
>
>
> Oops. I missed the 3 group part as it wasn't depicted in the design
> matrix. I would still add 2 columns for group. I've always been
> instructed to include the main effects in the model when including the
> interaction.
>
>
>
> I think I needed to provide a little more information in my original
> post. For the contrasts, I was under the impression that EV2 and
> EV3 in my design already specified the interaction between groups
> 1&2 and condition (EV2) and between groups 1&3 and condition (EV3):
>
> EV1(c) EV2(gXc_g1&g2) EV3 (gXc_g1&2)
> g1c1 1 1 1
> g1c2 -1 -1 -1
> g1c1 1 1 1
> g1c2 -1 -1 -1
> g2c1 1 -1 0
> g2c2 -1 1 0
> g2c1 1 -1 0
> g2c2 -1 1 0
> g3c1 1 0 -1
> g3c2 -1 0 1
> g3c1 1 0 -1
> g3c2 -1 0 1
>
> c1>c2 1 0 0
> intg1&2 0 1 0
> intg1&3 0 0 1
>
> If you have any more thoughts or suggestions they are appreciated.
>
>
> My apologies for missing the 3rd group part. The two interactions you
> have are two smaller interactions. You'd need an F test of c3 and c4 to
> get the interaction of group and condition.
>
> Sorry for the confusion.
>
>
>
>
> On 21/11/2013 3:36 PM, MCLAREN, Donald wrote:
>
>
>
> On Thu, Nov 21, 2013 at 8:31 AM, Greg Reckless
> <[log in to unmask]
> <mailto:[log in to unmask]>
> <mailto:[log in to unmask]
> <mailto:[log in to unmask]>>> wrote:
>
> Dear FSL list,
>
> I have a 2(condition) x 3(group) mixed-design study. I
> have created
> a model and contrasts (attached .png file) based on the
> 2-way Mixed
> Effect ANOVA described on the FSL Wiki
>
> (http://fsl.fmrib.ox.ac.uk/____fsl/fslwiki/GLM#ANOVA:_2-____groups.2C_2-levels_per_____subject_.282-way_Mixed_Effect_____ANOVA.29
> <http://fsl.fmrib.ox.ac.uk/__fsl/fslwiki/GLM#ANOVA:_2-__groups.2C_2-levels_per___subject_.282-way_Mixed_Effect___ANOVA.29>
>
> <http://fsl.fmrib.ox.ac.uk/__fsl/fslwiki/GLM#ANOVA:_2-__groups.2C_2-levels_per___subject_.282-way_Mixed_Effect___ANOVA.29
> <http://fsl.fmrib.ox.ac.uk/fsl/fslwiki/GLM#ANOVA:_2-groups.2C_2-levels_per_subject_.282-way_Mixed_Effect_ANOVA.29>>).
>
> For simplicity I have only included 2 subjects per group.
> Two
> COPEs from the first-level, representing the two levels of
> condition, were entered for each subject in the
> higher-level model.
>
> My questions are as follows:
> 1) Is this model correct and is it the most appropriate for
> a 2x3
> mixed design?
>
>
> Yes. Although I would add 2 columns for group for completeness.
>
>
> 2) Are my contrasts correct for testing the main effect of
> condition
> (Lvl.1>Lvl.2 and Lvl.2>Lvl.1 and the interaction effect between
> condition and group?
>
>
> Interaction contrasts aren't interactions. The interaction would
> be 0 0
> 1 -1 0 0 0 ...
> The contrast 0 0 1 0 0 0 ... tests if Lvl.1>Lvl.2 is significant in
> group 1.
>
>
> Thank you for your input!
> Greg
>
>
>
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