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help > RE: Covariance matrix
Apr 20, 2022 11:04 PM | Alfonso Nieto-Castanon - Boston University
RE: Covariance matrix
Hi Lillian,
Sorry, not directly from the Fisher transformed correlation values. You can get the correlation matrix R from the Fisher-transformed matrix Z by using:
R = tanh(Z);
but the covariance matrix requires also knowing the variances of those ROI timeseries so that is not possible. You can, of course, re-compute that covariance from the denoised timeseries, for example by reading the "data" variable from the ROI_Subject*_Condition*.mat files in the connproject/results/preprocessing folder, and then simply computing the covariance explicitly using something like:
load ROI_Subject001_Condition001.mat
rois = [10, 11, 12]; % select here the ROIs that you want to include in your analysis (note: only univariate ROIs)
[i,j] = ndgrid(rois);
C = arrayfun(@(i,j)data{i}'*data{j},i,j);
Hope this helps
Alfonso
Originally posted by omaomae:
Sorry, not directly from the Fisher transformed correlation values. You can get the correlation matrix R from the Fisher-transformed matrix Z by using:
R = tanh(Z);
but the covariance matrix requires also knowing the variances of those ROI timeseries so that is not possible. You can, of course, re-compute that covariance from the denoised timeseries, for example by reading the "data" variable from the ROI_Subject*_Condition*.mat files in the connproject/results/preprocessing folder, and then simply computing the covariance explicitly using something like:
load ROI_Subject001_Condition001.mat
rois = [10, 11, 12]; % select here the ROIs that you want to include in your analysis (note: only univariate ROIs)
[i,j] = ndgrid(rois);
C = arrayfun(@(i,j)data{i}'*data{j},i,j);
Hope this helps
Alfonso
Originally posted by omaomae:
Hi Alfonso and CONN experts,
Is there a way to obtain the covariance matrix for an ROI-to-ROI connectivity analysis, instead of just the Fisher's transformed correlation coefficients? Thanks!
Best,
Lillian
Is there a way to obtain the covariance matrix for an ROI-to-ROI connectivity analysis, instead of just the Fisher's transformed correlation coefficients? Thanks!
Best,
Lillian
Threaded View
Title | Author | Date |
---|---|---|
omaomae | Apr 18, 2022 | |
Alfonso Nieto-Castanon | Apr 20, 2022 | |