Friday, April 26, 2013

Crowdsourcing in manhunts can work

So much to post right now… but I will start with the easy stuff. Here is a news story for Nature on a preprint that seemed almost too topical to be true.


Despite mistakes over the Boston bombers, social media can help to find people quickly.

The social news website Reddit was left red-faced after mis-identifying the suspects for the Boston marathon bombings last week, raising questions about whether crowd-sourcing to gather information might do more harm than good in such situations.

But work by a team of scientists from the United Arab Emirates and coworkers in the US and UK offers a more upbeat message about the potential of social media to assist in crime investigations and societal searches. Last year they enlisted communities on networks such as Twitter and Facebook to look for five people in different cities around the world, and were able to find three of them within the 12-hour deadline imposed [1].

In a new preprint, the researchers now analyse the behaviour that made this possible. They say that participants responded to the urgency of the search not by sending out messages to their contacts in an indiscriminate, blind panic, but by becoming even more focused and directed about whom they contacted [2].

The experiment, by computer scientist Iyad Rahwan at the Masdar Institute of Science and Technology in Abu Dhabi and his colleagues, constituted the team’s entry in the Tag Challenge staged by the US State Department in March 2012. The Tag Challenge required teams to find individuals (posing as jewel thieves) in New York City, Washington DC, London, Stockholm and Bratislava within 12 hours. Participants were given only a ‘mug shot’ of each target wearing a T-shirt bearing the competition logo, released on the morning when the competition started.

Rahwan’s team used crowd-sourcing to find the targets, offering cash incentives to individuals for uploading photos of suspects to web and cell phone apps and for recruiting more searchers. Although they failed to locate the targets in London and Stockholm, the team out-performed all others and won the competition [1].

The results showed that “among this noisy stream of tweeting and retweeting, of news articles and messages being fired off to acquaintances around the globe, people are able to efficiently guide a message towards a target in a particular city”, says Rahwan’s colleague Alex Rutherford at the Masdar Institute.

The new analysis of the information provided by participants shows that communications such as tweets became more specific and targeted as the day of the competition approached, being increasingly directed towards other users in the target cities. “Despite increasing time pressure, and its associated cognitive load, people actually became more selective in their recruitment of others, making sure information is directed in an intelligent manner”, says Rahwan.

“This makes good sense to me, and it's what I would have expected”, says Peter Sheridan Dodds of the University of Vermont. In 2003 Dodds and coworkers conducted a social-search experiment [3] to route emails to a few target people worldwide – an electronic version of the famous ‘small-world’ experiment by psychologist Stanley Milgram in 1967, in which he asked random people to forward letters to addressees identified only by name, profession and city [4]. “In our small-world experiment we found that successful searches were much more focused than unsuccessful ones and less likely to involve scattershot, connect-to-everyone attempts,” Dodds says.

Defence and security organizations have a growing interest in these outcomes. In 2009 the US defence research agency DARPA staged the Red Balloon Challenge, in which competitors were challenged to locate ten red weather balloons tethered at random locations all over the US. That challenge was won by a team at the Massachusetts Institute of Technology led by Manuel Cebrian, who collaborated with Rahwan and colleagues for the Tag Challenge. The MIT team found the red balloons in 9 hours by harnessing social-networking media [5,6].

How does all this reflect on the search for the Boston bombers? Last week, Reddit users, acting on photographs of suspects posted by the FBI, collectively pointed the finger at several individuals who had nothing to do with the bombings, including an innocent student from Brown University. The eventual arrest of Dzhokhar Tsarnaev, who previously escaped with wounds after a shootout with police, came after a neighbour spotted blood on the tarpaulin covering the boat in which he was hiding.

“The Boston manhunt is an example of how things can go wrong”, says Rahwan. “It appears that information was very much misdirected. This may be, in part, due to the high profile of the event, which led everyone to want to help even if they were incapable or misinformed.”

“There may be a tradeoff between mass mobilization and effective mobilization of a more specialized group of reliable and well-informed individuals”, he adds. “Having too many people involved might actually make things worse.” He and his colleagues have begun to explore schemes for supporting the checking and verification of crowd-sourced reporting [7].

Even President Barack Obama has commented on the hazards of search efforts like those on Reddit. “Crowd-sourcing via social media can be incredibly powerful in mobilizing people”, says Rahwan, “but it is not a silver bullet.”

“I think the web-enhanced ‘collective detective’ is potentially very powerful and is here to stay”, agrees Dodds. “But we have to ensure that the distributed social search is always used for good, meaning for example that ‘bad’ actors cannot corrupt the search, and that good, well-intentioned actors are prevented from collectively generating errors leading to witch hunts.”

“There's a lot of wisdom in the crowd when people are actually aggregating independent pieces of information”, says David Liben-Nowell of Carleton College in Northfield, Minnesota, a specialist on the searching of social networks. “But when purported information is amplified and echoed by people without truly independent information being collected, as seemed to happen in the Reddit case, then we may end up with the folly of the mob instead.”

In situations like that, says Dodds, “unofficial efforts are very important, but the onus is now on governments to create and maintain distributed social search sites that allow the public to aid in finding people. A system should already be in place that is transparent and sophisticated, and that allows for the public to provide analysis, not just photos.”

“It's not just for finding bad guys”, he adds. “Missing children are an obvious example.”

“With any kind of task like this one, we have to accept that there's a tradeoff between the risk of a false negative and a false positive”, says Liben-Nowell. “As a society, we have to think carefully about where we want to be in that spectrum.”

1. Rahwan, I. et al., IEEE Computer April, 68-75 (2013).
2. Rutherford, A. et al., preprint
3. Dodds, P. S., Muhamad, R. & Watts, D. J. Science 301, 827-829 (2003).
4. Milgram, S. Psychology Today 61, 60-67 (1967).
5. Tang, J. et al., Commun. ACM 54, 78-85 (2011).
6. Rutherford, A. et al., Proc. Natl Acad. Sci. USA 110, 6281-6286 (2013).
7. Naroditskiy, V., Rahwan, I., Cebrian, M. & Jennings, N. R. PLoS ONE 7, e45924 (2012).

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