Criminology

Nice day for a crime

In the Montréal area, violence increases with the temperature. For example, an average of 64 assaults are committed daily when it is 30°C, compared to 55 when it is less than 23°C. Similarly, perpetration of sexual aggression has a direct link to hours of daylight. These findings were made by criminologist Étienne Blais in a study of connections between the weather and criminality, the results of which will be published shortly in the Revue internationale de Criminology comparée et de police scientifique . His research, funded by Environment Canada, was based on 160,000 reports by the Montréal Urban Community Police Department drafted between 1995 and 1998.

As far as Étienne Blais is concerned, there is no doubt that weather conditions have a direct influence on criminal activity. “Crimes against persons increase when it's warmer. This is just as true in January as it is in July. In the winter, 48 assaults are committed each day when the thermometer rises above 4°C, compared to 42 when it falls below ­–10°C. Conditions such as rain and wind have the opposite effect.”

The research, which he conducted at the Université de Montréal School of Criminology, where Mr. Blais is working on his doctorate, also shows a marked increase in criminality on the first few days of each month. The author points out that this increase corresponds to the time when social assistance cheques are sent out. “Right behind the day's maximum temperature is the cheque mailing variable,” he notes. The day the cheques are received, there is an average 61 assaults, as against fewer than 50 on other days.

The phenomenon can be explained by routine activities theory, which criminologists are very familiar with. According to this theory, people go out more during fair weather, which results in an increase in interactions between people, and thus also an increase in the risk of interpersonal conflicts. What is innovative about Mr. Blais's research is that it includes daily activities. “Most studies on this establish a link between weather and criminality on a monthly or annual basis. We have found that it is more informative to analyze it daily,” notes the student, who is working under the direction of criminologist Marc Ouimet. “As a result, we have compared criminal acts and weather conditions based on daily weather reports provided by Dorval.” Moreover, an earlier study by Mr. Ouimet showed that assaults in Québec were 13 times more frequent on weekends (Friday, Saturday, Sunday) than during the week. This time, they wanted to know whether the impact of long holidays was significant. The answer came back negative. “Long holidays have no measurable effect on criminality,” Etienne Blais notes. “But highway accidents show a sharp upturn.”