Facebook missed 83 percent of political ads run on Facebook, according to a joint study between researchers at New York University and KU Leuven in Belgium.

The researchers examined 33.8 milion ads that ran on Facebook between July 2020 and February 2021, finding that in 189,000 cases when Facebook reviewed an ad to check whether it should be treated as political, it was wrong 83 percent of the time. 

This included 117,000 cases where Facebook’s detection system failed to flag ads that should have been treated as political, and 40,000 ads that were mistakenly flagged as political when they were not.

The researchers also identified over 70,000 political ads running on Facebook during a temporary ban on political advertising that Facebook had imposed during the US presidential election, many of them by organisations that had only run political ads on the platform.

Facebook’s performance varied across different countries. It had the most success in filtering ads correctly in the US and New Zealand, where only one percent of ads slipped through the net. However, Facebook achieved its worst score in Malaysia, where 45 percent of ads remained under the radar.

The researchers warned that these shortcomings could lead to political manipulation, as users who see ads without a political disclaimer may not be aware that their intent is to influence them. 

They also noted that Facebook’s enforcement of the policy relies heavily on detecting keywords in ads under an automated system, although staff also play a role in moderating the content.