The purpose of this study was to investigate differences in personality traits among violent, theft, and illegal drug use criminals, comparing them with normal adults. Inmates (N = 645) and normal adults (N = 4546) in Japan responded to a questionnaire, including the Big Five personality traits. Results indicated that violent criminals tended to show lower Agreeableness and higher Extraversion than other criminals. Theft criminals tended to display low Conscientiousness. Illegal drug use criminals showed higher Extraversion and Openness. Inmates tended to show higher Extraversion, Agreeableness, Openness, and Conscientiousness than normal adults. Characteristics of personality traits of criminals were discussed.
There is a certain number of criminals who are imprisoned again after completing their jail terms and getting out of prison. For example, in the United States, a study of offenders, who were released from prison after serving a sentence of imprisonment in 2005, reported that 49.3% of offenders were rearrested within 8 years (Hunt & Dumville, 2016). In Japan, among those who were released from prison in 2006, the ratio who became inmates again, within 10 years, was 47.6% (Research and Training Institute, Ministry of Justice, Japan, 2016). Taking the above fact into consideration, how The Ministry of Justice, Japan, will prevent the repetition of crimes is a major challenge for the construction of a society where people can live safely in peace. There are various factors involved in committing a crime; however, to prevent re-offending, it is necessary to take an effective approach to each individual's problem, as well as to give guidance and support to overcome their problems. Therefore, Japanese prisons are seeking to enhance effective treatment based on research, according to individual offender's characteristics. This study examines personality characteristics of criminals for each type of offense, comparing their personality traits with normal adults. Personality traits play an important role to understand the addictive nature and genetic factors of criminals because of their stability across the lifespan and relationships with genes and the central nervous system (Miller, Lynam, & Leukefeld, 2003). Many psychologists now agree that the Big Five personality traits (Goldberg, 1990; McCrae & John, 1992) constitute an important overall personality structure of an individual's personality. The Big Five personality traits represent Openness (e.g., intellectual curiosity and creativity), Conscientiousness (e.g., orderliness and persistence), Extraversion (e.g., sociality and positive affect), Agreeableness (e.g., cooperation and trust), and Neuroticism (e.g., anxiety, depression, and emotional instability), and their scores are relatively stable across the life span (Roberts & DelVecchio, 2000). The five-dimension structure is found across different cultures (e.g., McCrae, Terracciano, & 78 Members of the Personality Profiles of Cultures Project, 2005) and a behavioral genetic study also supports them (Yamagata et al., 2006). The Big Five personality traits link to antisocial behaviors. Largescale longitudinal studies in Estonia (Mõttus, Guljajev, Allik, Laidra, & Pullmann, 2012) and in the United Kingdom (O'Riordan & O'Connell, 2014) showed that oncoming antisocial behaviors are significantly affected by low Agreeableness and Conscientiousness, and high Neuroticism. Meta-analytic research, aggregating 15 studies (Miller & Lynam, 2001) and 30 studies (Jones, Miller, & Lynam, 2011), also concluded that low Agreeableness and Conscientiousness, and high Neuroticism predicts antisocial behaviors.