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Depression linked to violent crime
Researchers also compared the odds of violent crime conviction among 15,534 half-siblings and 33,516 full siblings of depressed people, compared to the general population.
In the second study, they looked at a sample of 23,020 adult twins born between 1959 and 1986, who had participated in an adult or child and adolescent Swedish Twin study. They were asked to fill in a questionnaire in 2005 to measure depressive symptoms using a recognised depression scale, and they were then followed for any violent outcome through linkage to the Crime Register. The aim of this second study was to assess whether any association between depression and violent crime could be due to common genetic or environmental factors.
What were the basic results?
In the first study, researchers identified 47,158 individuals (17,249 men and 29,909 women) with outpatient diagnoses of depression between 2001 and 2009. The average age of diagnosis was 32 years for men and 31 for women. They were followed for an average of three years.
During the follow-up period, 641 men (3.7%) and 152 (0.5%) women with depression were convicted of committing a violent crime, compared with 1.2% of men and 0.2% of women in the general population.
After adjusting for various sociodemographic factors, they calculated that individuals with depression were three times more likely to be convicted of a violent crime compared to people in the general population (odds ratio (OR) 3.0, 95% confidence interval (CI) 2.8 to 3.3).
In people with either a previous criminal history, or a history of substance abuse or self-harm, the risk of being convicted for a violent crime was highest.
The odds of violent crime in brothers and sisters of people with depression were also significantly higher than in the general population, after adjusting the results to take into account age, sex, low family income and being born abroad:
- half-siblings (adjusted OR 1.2, 95% CI 1.1-1.4)
- full siblings (adjusted OR 1.5, 95% CI 1.3-1.6)
This, say the researchers, suggests that family background may be a confounding factor (confounder) in association between depression and a criminal conviction.
In the twin study, 88 violent crimes were recorded in the 5.4 years of follow-up.
Depressive symptoms were associated with a slightly increased risk of violent crime (hazard ratio (HR) 1.09, 95% CI 1.06 to 1.13).
How did the researchers interpret the results?
The researchers say that even after adjusting their findings for possible confounders, such as genetics and early family background, a diagnosis of depression modestly increased the risk of violent crime.
They argue that clinical guidelines should consider recommending violence risk assessment in certain subgroups with depression.
This was a large, well-conducted study that found an association between depression and violent crime. However, there were several limitations. As the authors point out, it did not include people who only go to their GPs - rather than psychiatric services - with depressive symptoms, or people who required inpatient admission for depression, so the results may not represent all people with depression.
Also, it was only conducted in one country, so the findings may not be generalisable to others.
As the authors say, they had no information about the treatment their patients had or were undergoing, so we cannot know how much treatment for depression was a factor in the findings.
The study did its best to take account of confounders that might influence the risk of violent crime, or explain both a diagnosis of depression and the likelihood of committing a crime, including family background. It is always possible that both measured and unmeasured confounders, such as early trauma or poor care as a child, can influence the results.
It's also worth noting that depressed people were found to be more likely to be convicted of crimes - not that they actually committed more crimes. Given the nature of depression, which is associated with feelings of guilt and hopelessness, it is possible that depressed people are less likely to try to avoid being caught and less likely to try to avoid a conviction - for example, by seeking legal advice.
The results of this study would appear to suggest that current UK clinical guidelines on depression may benefit from being amended, by including advice on the small risk of violence in depressed people. They certainly shouldn't be taken as "proof" that all depressed people are dangerous.
If you or someone you know is suffering from symptoms of depression, it is important to talk to a healthcare professional.
"Depressed people are three times more likely to commit a violent crime," the Daily Mirror reports. Research into Swedish crime and medical data found that depression was linked with an increased risk of a person committing a violent crime.
Links to Headlines
Depressed people are three times more likely to commit a violent crime, research shows. Daily Mirror, February 25 2015
Depression linked to violent crime, study finds. BBC News, February 25 2015
Depression to blame for 46,000 violent crimes a year, says Oxford University. The Daily Telegraph, February 25 2015
Links to Science
Fazel S, Wolf A, Chang Z, et al. Depression and violence: a Swedish population study. The Lancet - Psychiatry. Published online February 25 2015
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