Before revision:  combining data from different scanners and sites for structural covariance analysis in a naive manner should be avoided,  (2) surface area and volume should be preferred as morphological measures of structural covariance over cortical thickness , and (3) some analysis of robustness of the results should be performed for every structural covariancestudy .
After revision:  combining data from different scanners and sites for structural covariance analysis in a naive manner should be avoided, particularly if sites differ in image resolutions, demographics, or preprocessing; (2) surface area and volume should be preferred as morphological measures of structural covariance over cortical thickness , and (3) some analysis of robustness of the results should be performed for every structural covariancestudy .