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Effects of Information Cascades during the Paris Terrorist Attacks

PorteOuverte. Open Door. Such a simple phrase carried powerful connotations in the wake of the series of terror attacks in Paris. After the set-off of explosions by suicide bombers near the Stade de France in Saint Denis and a round of shootings near the cafe “Le petit Cambodge”, Parisian government officials quickly ordered a state of emergency. Citizens were instructed to stay at home, however many tourists in the area became stranded as a result of this lockdown. Flights were cancelled, trains were closed down, and borders closed in attempt to keep the terrorist groups within the country. Soon after, the hashtag #PorteOuverte quickly became trending worldwide as native residents of Paris voluntarily opened their homes to tourists stranded by the attacks and lockdown.

Because twitter is already a social-network, we can see the effects of a network-cascade in the system. We can define a hashtag as “trending” if the cascade of users in the system have adopted tweeting the hashtag. We can additional define that the hashtag has surpassed a certain threshold in which after enough people have garnered initial support in retweeting the hashtag, more and more people will retweet the hashtag regardless of its relevancy or importance. It is clear that the “wrong decision” can easily be adopted as a decision by users in the twitter network, as evident in the #porteouverte tweets that had well-intentioned users haphazardly posting their home address on the internet. While smarter users asked for a direct message before giving out their address to strangers, many other users had simple hopped on the bandwagon and tweeted their address without concern. Even users not living in Paris have started using the same hashtag as a message of support; however, this behavior, although non-malicious in intent, actually is also a detriment to the people who were truly desperate for a place to stay as these messages clogged up the search results on twitter. Overall, we can see the information-cascade effects on a real-world event model, in which users in a social network began to adopt a certain trend of tweeting #porteouvertes after enough initial users caused the hashtag to become trending. The decision to join other users in this mass tweet may have been a good or bad decision based on context, but this tragedy is now a prime example of the powerful effects of information cascades.



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November 2015