A simple self-reflection intervention boosts the 1 detection of targeted advertising 2

4 Online platforms collect and infer detailed information about people and their 5 behaviour, giving advertisers an unprecedented ability to reach specific groups of 6 recipients. This ability to “microtarget” messages contrasts with people’s limited 7 knowledge of what data platforms hold and how those data are used. Two on8 line experiments (total N = 828) demonstrated that a short, simple intervention 9 prompting participants to reflect on a targeted personality dimension boosted their 10 ability to correctly identify the ads that were targeted at them by up to 26 percent11 age points. Merely providing a description of the targeted personality dimension did 12 not improve accuracy; accuracy increased when participants completed a short ques13 tionnaire assessing the personality dimension—even when no personalized feedback 14 was provided. We argue that such “boosting approaches,” which improve peoples’ 15 ability to detect advertising strategies, should be part of a policy mix aiming to 16 increase platforms’ transparency and give people the competences necessary to re17 claim their autonomy online. 18