Thank you Michael, that was enlightening. The answer is no, we can not assume that there is a linear relationship between these diagnostic groups.
So how should a model be testing a continuum of GM abnormalities between these 4 diagnostic groups using a multiple regression model ? I really can not think of anything at this point.
Cheers
Cagri
On Thu, 5 Jan 2012 10:56:47 -0600, Michael Harms <[log in to unmask]> wrote:
>Whether or not a linear model relating the groups makes sense depends on
>on the specific groups, so I don't know whether it makes sense in your
>context or not. I'll just note that modeling a linear relationship
>between groups is a specific hypothesis that assumes that each step up
>in the "group" variable yields an identical change in the dependent
>variable (since all the groups were themselves spaced by a delta of 1
>unit). This is *not* the same as hypothesizing that there is merely a
>continuum in the DV such that 1 > 2 > 3 > 4 (or 1 < 2 < 3 < 4).
>
>cheers,
>-MH
>
>On Thu, 2012-01-05 at 16:38 +0000, Cagri Yuksel wrote:
>> Hello Michael,
>>
>> Thank you for your answer. Yes, I realized my mistake about the interpretation of the results right after I sent the message.
>>
>> These diagnostic groups are related and this analysis is to test an a priori hypothesis about a possible continuum of GM abnormalities in these groups, that's why I was thinking a linear model.
>>
>> Do you think it makes sense ? Do you have other suggestions?
>>
>> Thank you again,
>>
>> Cagri
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