Many of the personality traits that are commonly found in criminals are to be expected: aggression, narcissism and defensiveness, for instance.

But a new study has revealed another, more surprising characteristic that you might associate with those with a more sunny disposition.

Openness, which experts define as a willingness to try new experiences, is also commonly seen in the characters of offenders, research has found.

Experts at Babes-Bolyai University in Romania conducted interviews with inmates at a high security prison, and compared their personality traits with a group of matched controls in the community. 

Speaking of the prisoners' shared enjoyment of new experiences, the researchers said this may also increase their willingness to take risks, which could lead to criminal behaviour. 

However, openness did not appear to predict reoffending, indicating that this trait may be more relevant to initial criminal acts.

This characteristic is the only 'bright triad' — positive — personality trait that increases the chance of offending, the study found.

Extraversion, which is typically associated with sociability and assertiveness, was lower in both first-time offenders and repeat offenders compared to individuals without a criminal history.

Also surprising was the association between neuroticism and criminal behaviour.

 Neuroticism — a tendency to respond poorly to stress, resulting in anxiety, anger, and sadness — was consistently linked to both first-time offending and reoffending.

This suggests that emotional instability may be a risk factor for engaging in criminal activities and continuing to do so over time.

Overall, the study found the strongest predictor of criminality was 'dark triad' traits — higher levels of emotional instability, risk-taking, as well as deceitfulness.

'Each individual combination of these traits relates to criminal behaviour and to the likelihood of reoffending in significant ways,' says Professor Laura Visu-Petra, from Babes-Bolyai University, who led the study.

'Individuals involved in criminal activities report emotional instability (high neuroticism), reduced positive emotions, lower assertiveness, and diminished sensitivity to social feedback (low extraversion),' she told PsyPost.

Interestingly, the study found that extraversion — typically associated with sociability and assertiveness — was lower in both first-time offenders and repeat offenders compared to individuals without a criminal history.

Meaning criminals are more likely to be reserved or less outgoing than their peers.

Rather unsurprisingly, the researchers also found that sadism — the tendency to enjoy causing harm to others — was linked to first-time offending but not reoffending.

The scientists caution that not everyone with 'dark triad' personality types will become a criminal.

In fact, Professor Visu-Petra says those with these traits are also often found in high-flying corporate jobs. 

Other dark traits like a lack of empathy, vindictiveness, and a sense of deserving more than others did not emerge as significant predictors of criminal behaviour.

The study, published in Scientific Reports, included 578 participants, split into two groups: a general community sample of 282 individuals and a group of 296 inmates from two maximum-security prisons in Romania.

The inmate group was further divided into two subgroups: first-time offenders (129 people) and repeat offenders (167 people).

Unusually, two of the researchers observed the inmates from inside the prison in order to get a representative picture of prisoners' personality traits. 

The researchers hope that the study will help people inform how staff treat offenders in prison.

'This will impact not only practitioners working in correctional facilities, but also contribute to a safer and more accepting community for us all.'