Hi Martin,
 Each subject has 3-6 timepoints. They are all about one year apart.  Here's an example of the discrepancy: one subject with  5 timepoints had volumes that ranged from 2.2-2.4. However, from the long_mris_slopes command, the temporal average volume was calculated to be 1.67. Thanks for your help!

-Shannon K. 

On Thu, Sep 27, 2012 at 6:21 AM, Martin Reuter <mreuter@nmr.mgh.harvard.edu> wrote:
Hi Shannon,

long_mris_slopes works for surface maps (both thickness and volume
should work). In both cases it should compute the temporal average.

I have another scripts that works for stats files (long_stats_slopes) in
the same way.

How many time points do you have, how far apart (equally spaced?).

Best, Martin

On Wed, 2012-09-26 at 14:59 -1000, Shannon Kogachi wrote:
> Hi Martin,
>    When I used the long_mris_slopes  command for the thickness, the
> average thickness calculated in FreeSurfer was pretty similar to
> averaging the values in FreeSurfer. Does this command only work
> thickness measures and not for volume or area? Thanks!
>
> -Shannon
>
> On Wed, Sep 26, 2012 at 2:49 PM, Martin Reuter
> <mreuter@nmr.mgh.harvard.edu> wrote:
>         Hi Shannon
>
>         You probably mean average thickness.
>         My scripts compute the temporal average from the linear fit
>         (at mid time), which can be differed from simply averaging
>         values.
>         Best Martin
>
>         Shannon Kogachi <skogachi@gmail.com> wrote:
>                 Hi,
>                  I had a question about how the temporal average is
>                 calculated for subjects with multiple timepoints. I
>                 used the long_mris_slopes command on a longitudinal
>                 set of data. However, when I compared the average
>                 volumes calculated through this command to the average
>                 volumes calculated in excel after extracting the same
>                 vertices at the individual timepoints, these values
>                 did not match up. The average volumes calculated
>                 through long_mris_slopes were smaller. Please let me
>                 know if there is a way to explain this discrepancy.
>                 Thank you!
>
>                 -Shannon K.
>
>
>
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