Figures used by Amsterdam city council to justify an experiment with arming some of its street wardens with truncheons were wrong, officials have admitted following research by campaign group Controle Alt Delete.

The figures used by officials suggested that wardens – known as boas in Dutch – are far more likely to face being attacked than they were in reality, and now mayor Femke Halsema has told councillors the information about physical violence was “wrongly registered”, the Parool reported on Tuesday.

One option on the registration form – “not relevant” – was counted by the system as a physical attack, an error discovered by Controle Alt Delete, which monitors police and warden-related violence.

The wrongful figures, which suggested eight in 10 wardens had been confronted with aggression and violence, were used as a reason to provide some wardens with batons following a campaign by their union.

The real figure should have been four to five, which Halsema said is still high and still justified the experiment with giving wardens weapons.

According to Controle Alt Delete, the 400 Amsterdam wardens were on the receiving end of 158 incidents involving physical aggression in 2025.

The experiment ended in December and the mayor is currently assessing whether or not they should become a permanent part of some wardens’ kit.