Basic demographic and health characteristics of the full VETSA sample are comparable to U.S. census data for similarly aged men (Kremen et al. 2006). The VETSA1 MRI subsample did not differ significantly from the full VETSA sample with respect to the above demographic measures, nor were there significant differences between MZ and DZ twins. There were no significant group differences for the mean number and variance of pack-years or brain morphometric measures between MZ and DZ twins.
