The conceptualization of the underlying liability dimensions of psychiatric disorders has mainly focused on common Axis I disorders, but recent studies have expand these dimensions to include other less common disorders and Axis II personality disorders (Kendler et al, 2011; Kotov et al, 2011; Keyes et al, 2012; Markon, 2010; Roysambe et al, 2011). These studies provide support for externalizing and internalizing liability, though some studies found separate but moderately correlated externalizing and internalizing factors for Axis I and Axis II disorders (Kendler et al., 2011; Roysambe et al., 2011).
