Hi Doug and Donald, Again many thanks for the advice. With regard to the analysis described previously - I have n=21 in my control group while P1=4 patients, P2=7 patients, P3=3 patients and P4=5 patients. Given that i have small numbers I elected to compare only 2 patient groups (p1 and p4) rather than all 4.
My aim was to show that P4 patients (higher level of endogenous factor) are more affected (eg smaller area and greater thickness-age decline compared to controls) than P1. Given that as Donald points out that (c-p1) - (c-p4) is like comparing p1 and p4 directly, I did the latter but there is nothing significant. However when i compare p1 to controls and then p4 to controls separately i see nothing signficant in the p1 analysis but significant results in the p4 analysis - this makes sense as the p4 gp are more affected than the very mild p1 gp. My questions are: 1) why the difference in results between the two analyses (? due to larger overall group in second analysis) 2) is the latter analysis valid ? Thanks for your help. Mahinda _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.
