No no sorry for the misunderstanding. Either you correct by division with subic_vol = average_eTIV_allsample * subic_vol / eTIV_subject OR y0ou correct by regression. Only if you do regression, I’d use (eTIV_subject - average_eTIV_allsample) rather than eTIV_subject directly (and the same for all other variables: age, etc). Again: the result will be the same, but if you look at the residuals (plus the global intercept), demeaning will leave you with something that looks like the volume of a subiculum. Cheers, /Eugenio
Juan Eugenio Iglesias Senior research fellow CMIC (UCL), MGH (HMS) and CSAIL (MIT) http://www.jeiglesias.com
From: freesurfer-bounces@nmr.mgh.harvard.edu on behalf of Steve Petersen marfneuro@gmail.com Reply-To: Freesurfer support list freesurfer@nmr.mgh.harvard.edu Date: Wednesday, April 22, 2020 at 12:39 To: "freesurfer@nmr.mgh.harvard.edu" freesurfer@nmr.mgh.harvard.edu Subject: Re: [Freesurfer] Correlation between Hippocampal subfields - behavioural test
External Email - Use Caution Dear Eugenio,
Thank you for your quick response. Sorry but I am not completely sure if I understood correctly your response. What do you mean with "demeaning" the eTIV first?.
If I understood, a good choice would be to correct the subic_volume before perform the regression using the folliwng formula:
subic_vol = average_eTIV_allsample * subic_vol / eTIV_subject
Thank you.
Best,
Steve.
El mié., 22 abr. 2020 a las 17:35, Steve Petersen (<marfneuro@gmail.commailto:marfneuro@gmail.com>) escribió: Dear Freesurfer experts,
I would like to perform a correlation between the volume of subiculum and some behavioural measures. Before making that correlation, is it necessary to correct the subiculum volume with the eTIV? I have thought of doing it by scaling the subiculum volume as follows:
subic_vol = mean_eTIV_group * subic_vol / eTIV_subject Is correct??
mean_eTIV_group = eTIV average of the group to which the subject belongs.
Thanks in advance.
Best regards,
Steve.