I see, thank you very much anyways.
I am wondering if it's my misinterpretation of the reviewers comment, so I am copying the exact words of the reviewer to give a better idea about what is asked from us (I just changed the group names):
" the examination of a potential continuum of abnormalities between these groups is likely the more adequate approach. Given the limited statistical power of this study this is probably best examined in the context of a multiple regression model with a group variable (e.g., Group X = 4, Group Y = 3, Group Z = 2, healthy volunteers = 1) and an independent estimation of (potentially unequal) group variances. Given the strong a priori evidence for a continuous increase in gray matter deficits in prefrontal and temporal cortices over groups, one-sided testing of such a model appears legitimate."
Many thanks
Cagri
On Fri, 6 Jan 2012 08:07:23 -0600, Michael Harms <[log in to unmask]> wrote:
>I've never had to test for an "ordered continuum" between groups, so
>maybe others will chime in. Perhaps you could do the conjunction of the
>regions that satisfy 1 > 2, 2 > 3, and 3 > 4 ?
>
>good luck,
>-MH
>
>On Fri, 2012-01-06 at 12:34 +0000, Cagri Yuksel wrote:
>> 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
|