it is invalid because the sum of them was not 0.

but I also want to know if the following are right:

[-1 -1 -1 -1 4]

and what it mean.

                    Thank you very much



-----原始邮件-----
发件人:"Robin CHARK" <[log in to unmask]>
发送时间:2005-09-28 19:53:52
收件人:[log in to unmask]
抄送:(无)
主题:Re: are the two designs same?

One follow-up question. If I want to test the significancy of the first 4
conditions only, can I define it as [1 1 1 1 0]?
Thanks.
Robin


> hi
>
>> Dear all:
>>
>> If I had a five conditions fMRI experiment, and made the following two
>> t-contrasts using spm2 :
>>
>> [1 1 1 1 -1] and [1 0 0 0 -1;
>>
>> 0 1 0 0 -1;
>>
>> 0 0 1 0 -1;
>>
>> 0 0 0 1 -1]
>>
>> Are they all valid? And are they the same? If not, what are they
>> meaning separately?
>>
>> Tank you very much!
>>
> well, they are not all valid and they are not the same ..
> 1. When you enter a contrast, the sum of coef must be 0 and thus [1 1 1
> 1 -1] is invalid (you can try but SPM contrast manager will refuse to do
> that) .. if you want to oppose one condition against the others the
> correct contrast would be [1 1 1 1 -4]
> 2. in the second case you test if any of these contrasts (or
> combinations) is significant .. but those ones are correct as they all
> sum up to 0
>
> best
> cyril