How are demonstrators counted?

In Marseille, on Tuesday 31 January, the police counted 40,000 demonstrators against the pension reform, the CGT 205,000, and in Nantes 28,000 according to the police and 65,000 according to the trade unions. The science of crowd counting is subtle and more complex, characterized by changes in movement and density during demonstrations. Why is there such a discrepancy in the numbers? The world takes into account the methods used by the police, trade unions or independent firm Occurrence.

Manual calculation for the police

The calculation by the police is done manually “click” activated every time dozens of people pass by using a counter. is carried out by “loyal staff” usually placed at a high point, “A few hundred meters from the departure point” The demonstration appoints the Ministry of Internal Affairs.

A second high point can be installed “half way” For greater mobilization, the Place Beauvau continues. In addition, after viewing the videos, the police can record the demonstration and conduct a recount later.

Calculations for trade unions

Counting on the Union side is done manually by purely human means. Activists stationed along the procession count the rows of demonstrators one by one. “They estimate by eye how many people are in each row and multiply these two numbers”explain Franceinfo.

Call a tech for an independent firm

Since 2017, an independent calculation has been created by the firm Occurrence, which provides the figures recorded during demonstrations, including to the media. The world is part of

The event uses technology “Eurecam”especially used for missions “security at airports or fanzones”, concludes with The world its president, Assaël Adary. Sensors placed on the transition of the march create a field with a virtual line. Anyone crossing this line is counted by these sensors.

People’s movements in demonstrations are more complex than in a fanzone for a sporting event, with differences in density or visibility, for example, with a margin of error of 30-40%, according to Mr Adary. However, this is corrected by a margin of error “manual microcalculations”especially when the density is high or when an item such as a smoke bomb obstructs visibility.

“When we count again, we have to add almost systematically” Demonstrators, the cabinet chairman said: “At the end of the shows, we present a kind of spreadsheet to the media, where we see the numbers observed in eight-second slices, the number given by the sensor, and the corrected number. »

Out of forty demonstrations, the figures recorded by Oshma were 15 to 20% higher than those reported by the prefectures, and 220% to 250% lower than those reported by the unions.

Which method is the most reliable?

Can we determine which method is closer to reality? The Commission tried to answer this in 2014. Commissioned by Dominique Schnapper, director of scientific research at the Ecole des Hautes Etudes en Sciences Sociales (EHESS), Pierre Muller, chief inspector of INSEE, and Daniel Gaxie Paris, professor of political science. Counting in the best way to study at the police headquarters.

Although a “unavoidable margin of error”, these three personalities concluded that the system used by the police is the least flawed. The authors of the study, however, recommended giving the police a range of information rather than an exact number. In addition, the study published in 2015 did not take into account the methods of the firm Occurrence, which began independent calculations in 2017.