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Hi Javier,

when you do the exact same thing on the exact same computer the results are going to be exactly the same. There is no magic involved.

Another idea: have a look at how you compiled your binaries. Rounding errors of floating point computations are known to be very slightly different on different CPUs with different instruction sets, and for different compilers. Even when using the same SPM version/

The difference in location of a few mm is suspect though and probably unrelated to floating point rounding errors. Check your preprocessing scripts and reslice/bounding box settings very carefully.

What are you trying to accomplish by the way?

Cheers,

Bas

Op 20-02-12 10:35, Javier Elkin schreef:
[log in to unmask]" type="cite"> Hello SPM users,

We are currently encountering a problem with inter-rater reliability in our data.
The design is a very basic fMRI picture presentation block design. We are 2 
people doing the same exact analysis on the same exact data and raw data
on 2 different computers and are finding tiny discrepancies between our results 
(e.g. the x, y, z coordinates are off by a difference of 1 or 2, the coordinates 
sometimes come in different orders  of significance, the set-level value is off by 0.001). 

Basically there are no HUGE differences as pretty much the same areas are being 
implicated but we cannot understand why our machines are giving us different outputs. 
We have tried to account for this difference by

1. restarting ALL analyses from raw data (no difference)
2. switching computers and doing all the work outloud on each other's computers
    simultaneously 

Since when doing this latter solution we found each other's results (i.e. Our results were the
same based on the computer we were using, so the computers were receiving the exact same
input at the same time from raw and gave the results they gave before) we thought it might simply
be a matter of applying the latest spm update to the other computer but the site has been down for 
a couple of days.

What we need from the SPM community:

1. Can anyone email the latest update (Apr-2011)? Does it fit in an email?
2. Any other possibilities/suggestions as to why this problem is happening?

Any hints or advice will be most appreciated,

Sincerely

Javier Elkin 


  
    






-- 
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Dr. S.F.W. Neggers
Division of Brain Research
Rudolf Magnus Institute for Neuroscience
Utrecht University Medical Center

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