Before revision:  To understand our observations of low reliability, we estimated a measurement error covariance, and we show that it is largest in cortical thickness. On simulated datawe further demonstrated that stronger errors cause stronger attenuation of correlations and proportionally decreases reliability, which agrees with associations we observed in the real data. To our knowledge this study is the first highlight the problem of reliability and comparability in structural covariance . Practically, we suggest that (1)
After revision:  To understand our observations of low reliability, we estimated a measurement error covariance, and we show that it is largest when using thickness. With simulated data, we argue that cortical thickness is least reliable because of larger relative measurement errors . Practically, we suggest that (1)