By Telegraph Claim Overstates The Evidence
A recent article in the Daily Telegraph claimed that cannabis users are “twice as likely to be violent.” The claim was based on a systematic review by King’s College London that combined 63 studies covering more than 265,000 people.
Simon C Moore of Cardiff University, writing via The Conversation, argued that the headline overstates what the numbers can tell us. He noted that the claim echoed the dark days of Reefer Madness, a 1936 film that portrayed cannabis as a drug that could drive people to madness and murder.
The researchers did, indeed, find a link between cannabis use and violence. But Moore identified three reasons to be cautious: other factors that could explain the link, known as confounders; the way the studies were designed; and potential biases in how the data was gathered.
Confounders Could Explain The Link
Poverty, alcohol, other drugs and a difficult upbringing are all linked to violence in their own right, Moore wrote. Cannabis is also illegal in many places, and buying it can bring people into contact with people and places where violence is more common.
Some of these factors are more common among cannabis users, so these confounders could partly explain the link between cannabis use and violence found in the review.
“Ice cream sales rise and fall alongside drownings, yet nobody thinks ice cream causes drowning. Hot weather makes people eat more ice cream and swim more, linking the two. Cannabis and violence may be connected in a similarly roundabout way,” Simon C Moore of Cardiff University wrote via The Conversation.
What The Review Can And Cannot Say
The review did try to account for other factors, according to Moore. Even so, he maintained that the Telegraph’s headline went beyond what the underlying numbers can support.
Moore’s assessment was that the review’s findings show an association between cannabis use and violence, but that the design of the studies and potential biases in how the data was gathered leave room for alternative explanations.
For these reasons, Moore concluded that the claim that cannabis users are “twice as likely to be violent” overstates what the evidence shows.
