"Studies have shown that many irregular migrants embark on journeys without accurate or complete information about migration. In response, IOM and other organizations run information campaigns intended to inform potential migrants of the dangers associated with irregular migration and to facilitate informed decisions. The use of online and social media platforms for these campaigns has become increasingly popular in recent years, due to their potential for quickly reaching millions of people at low cost. While the evidence base for offline information campaigns has been gradually improving, it remains unclear how online communication campaigns affect potential migrants, and methodologies to do this remain underdeveloped. This report therefore presents results from a pilot impact assessment of an online campaign based on Facebook posts in Guinea, Nigeria and Senegal during September 2019 and February 2020 [.] Conclusion: Facebook ad campaigns can reach many people quickly. However, large audience sizes and relatively cheap costs come with a trade-off. The impact of an information campaign on potential migrants’ perceptions, attitudes, knowledge and behaviour remains largely unknown because many Facebook users that engage with the campaign do not fit the intended target group. The advantage of offline over online campaigns is that implementers have more control and information about who attends activities or who is exposed to campaign content. The engagement of users with campaign posts varies largely by audience and post characteristics. Campaign and social media teams are well advised to conduct pilot tests before scaling up activities. Pilot tests can inform a customized approach for each online activity on Facebook, and thereby maximize impact. In addition to A/B tests, lift tests may offer a useful opportunity to test the impact of Facebook posts. Compared to impact assessments of offline information campaigns, measuring the impact of Facebook ads on potential migrants presents several unique challenges, including: Many potential migrants are not on Facebook or do not use ad content to seek information about migration. Internet connectivity is also limited in many West African countries. While Facebook allows users to narrow down target groups, it is not clear whether those Facebook users that are exposed to the content fit the profile of potential migrants. Whether the intended target group is reached can be affirmed only through surveys, which have a low response rate; It is not possible to interview the same Facebook users several times to track changes in their perceptions. Engagement metrics like post reactions, link clicks or video plays can be useful indicators. However, these low-engagement metrics do not offer clear evidence of the short- or long-term effects on Facebook users." (Executive summary)