On Fri, 16 Oct 2009 13:45:08 +0200, Dorian P. <[log in to unmask]> wrote:
>Thank you for answering.
>
>Now I understand the reason behind that. But how can I investigate
>interactions amongst conditions in 2nd level without loosing the
>statistical power this way?
>
>The one-sample (and paired t-test) show activity without any doubt
>(FWE corrected, k=5). If I use ANOVA, instead, it will simply
>disappear even at p < 0.001. Previously I thought setting
>"independence = no" would be the same as doing the contrasts in 1st
>level. Apparently I was wrong. Can we conclude that ANOVA is producing
>false negatives and stick to analysis without interactions? What would
>you do in my case?
Make sure you model the effect of subject in your second level ANOVA.
You can get info on how to do that by searching the list like
anova AND "effect of subject"
or
anova AND "subject effects"
>
>Thank you.
>Dorian
>
>
>2009/10/16 Lily Liu <[log in to unmask]>:
>> When you contrast A > B in 1st level and make one-sample t-test in 2nd
level
>> , you treat A and B as within-subject conditions. But if you contrast A and
>> B separately in 1st level and bring them to two-sampled t-test, you treat A
>> and B as the between-subject conditions, which bring more variations and
is
>> less sensitive.
>>
>> Li Liu
>>
>>
>> 2009/10/16 Dorian P. <[log in to unmask]>
>>>
>>> Dear all,
>>>
>>> I am getting confused with results from different tests. If my
>>> understanding is correct, there should be no difference if I:
>>> (1) contrast A > B in 1st level and make one-sample t-test in 2nd level OR
>>> (2) contrast A and B separately in 1st level (contrast "1") and bring
>>> them to full-factorial (ANOVA) or two-sampled t-test.
>>>
>>> Well, this is not the case. Two-sample and full-factorial are
>>> producing different results (even when I set dependent measurements).
With
>>> one-sample t-tests I find strong activity (FWE corrected), which
>>> disappears if I follow way 2. Only the paired t-test produces the same
>>> identical
>>> result as the one-sample t-test.
>>>
>>> Can someone explain the differences between these tests?
>>>
>>> Does this suggest it's better to do many one-sample t-tests instead
>>> of a single ANOVA in 2nd level?
>>>
>>> Do ANOVA really loose statistical power (maybe because of degrees of
>>> freedom)?
>>>
>>>
>>> Any help is welcome. Thanks in advance.
>>
>>
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