"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.
It is important to stress from the outset that while the number of depressed people involved in a violent crime was above average, it was still small.
3.7% of men and 0.5% of women were convicted of committing a violent crime after being identified as clinically depressed, compared to 1.2% of men and 0.2% of women in the general population.
This was a well-designed study, but it’s important that the findings are not misinterpreted or used to add to the stigma of depression.
Also, the study does not show that depression causes crime. It only found an association between depression and a criminal conviction. It is possible that a third factor – such as poverty, unemployment or early trauma – can explain this link.
The study only included patients diagnosed and treated for depression by outpatient psychiatric services. People who required inpatient admissions and those treated by their GPs were excluded, so it may not be representative of people with different severities of depression.
If you are suffering from symptoms of depression, it is important to talk to your GP, especially if you find yourself lashing out at people. It’s important to remember that depression is treatable.
Where did the story come from?
The study was carried out by researchers from the University of Oxford and funded by the Wellcome Trust and the Swedish Research Council. Two authors declare financial ties with pharmaceutical companies, including Shire, Eli Lilly, Servier, Cephalon/Teva, Merck and GlaxoSmithKline.
The study was published in the peer-reviewed medical journal Lancet Psychiatry.
Most of the UK media’s coverage was fair and included comments from independent experts.
The exception was The Daily Telegraph, as its headline, "Depression to blame for 46,000 violent crimes a year", was dangerously misleading. This headline does not relate to the results of the study, which was conducted in Sweden. In addition, the study found an association between depression and convictions for crime, but it did not show that depression was "to blame".
What kind of research was this?
This was an observational study that looked at the risk of violent crime in people with depression. In a second study, the authors investigated the association between depressive symptoms and violent crime in a cohort of twins, to assess the potential role of genetic and environmental factors.
The authors say that depression is associated with a wide range of adverse outcomes, including suicide, self-harm and early death, but any association with violent crime is uncertain.
What did the research involve?
The authors conducted two studies on people from Sweden. The first compared the rates of violent crime in people with depression and their siblings, compared to the general population. The second study followed a cohort of twins, assessed any symptoms of depression in 2005, and followed them up to see if any committed a violent offence.
The first was a population study in Sweden of 47,158 people diagnosed with at least two episodes of depressive disorders between 2001 and 2009. Those requiring inpatient admission were excluded, as were those with other psychiatric diagnoses. They were age- and sex-matched to 898,454 people in the general population, to compare the odds of their being convicted of violent crime. They analysed the results, taking account of various factors – low income, immigrant status, history of self-harm, previous criminality, and drug and alcohol abuse.
Data on convictions for violent crimes was obtained from the country’s national Crime Register and defined as:
- attempted homicide
- aggravated assault
- common assault
- any sexual offence
- illegal threats or intimidation
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.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
The Daily Telegraph, 25 February 2015
BBC News, 25 February 2015
Daily Mirror, 25 February 2015
Links to the science
The Lancet – Psychiatry. Published online February 25 2015