Many studies of personality rely on self-report instruments, which are susceptible to biases and faking (Furnham, 1997). To address this issue, the current study included peer-report measures of neuroticism in addition to self-report measures. Achenbach et al. (2005) reviewed the literature and found that peer- and self-report measures of internalizing psychopathology and externalizing psychopathology correlated significantly, but that peer measures often had incremental validity. To the extent that peer measures yield different results than self-report measures, it suggests the importance of observable behavior, in addition to internal, cognitive processes (Achenbach et al.).
