Following the Boston bombings, anyone following the relevant feeds and hashtags would have seen a surge of contradictory stories and speculation, some important and true, others later exposed as nonsense. Twitter is both an enormous rumour mill, and invaluable source of valuable information. I could end this article here, but academics have been studying this question in detail since at least 2010, so I'm about to get a little technical.
Ever since the Osama Bin Laden raid was live-blogged, it has been clear that Twitter is allowing an explosion in 'citizen-witnessing'. Big events offline now often spike online shortly thereafter as 'Twitcidents'. Given the immediacy and ease of propagation, plausible misinformation often spreads very quickly causing a statistically significant change in the text stream. This is how trending topics are sparked - sudden change in the 'burstiness' of key words or phrases that an algorithm thinks is outside its normal distribution. (This is why words like 'the' and 'LOL' don't trend). For those of us scrolling a timeline full of interesting but unverified stories, it is hard to know what to trust.
According to James Surowiecki in his book Wisdom of the Crowds, collectives are a better way of arriving at certain kinds of truths under certain conditions: a diversity of opinion, independence, decentralisation, and aggregation.
Social media does not always meet these conditions. People share stories on Twitter for lots of reasons, and not always because they think it is accurate. Outlandish rumours often spread quickly, because they are interesting, and people like interesting things. During the London riots stories of tigers loose on Primrose Hill and the Army at Bank went viral, and this weight gave them a credibility it took hours to crack. Tweets by phoney accounts - including one of President al-Assad - have been picked up by major news outlets.
Generally, though, untrue stories are usually fairly short lived due to some of the Twitter user community acting as information brokers who will actively check and debunk information that they have found to be false or unreliable. Looking at the stories on Twitter during the Chiliean earthquake, one academic group found that Twitter weeded out falsehoods: 95 per cent of 'confirmed truth' tweets, were 'affirmed'; by users, while only 0.3 were denied.
By contrast, around 50 per cent of tweets later found to be false were 'denied' by users. A paper published this year by academics at Chicago looking at Twitter during the Arab uprising found that certain ordinary users rose to prominence through networked gatekeeping actions - those seen as useful and trustworthy sources tended to rise to the top, and then generate more traffic.
Although there is a self-correcting function, this can take some time, and given the networked nature of Twitter, misinformation often remain uncorrected within groups. The 2011 London riots were widely discussed on Twitter, and although the rumours - including the Tiger running around in NW1 - were dispelled, it was only after some time, and remained prominent within certain groups that may not have had such a diverse information source. (Or just didn't care).
The competition among journalists to get the scoop will ensure rumours continue to zip around. But there are ways to use Twitter to take advantage of the incredible amount of citizen journalism it offers. Twitter users play a number of different roles in exchanging information. They can generate information about events first-hand. They can request information about events. They can 'broker' information by responding to information requests, checking information and adding additional information from other sources and they can propagate information that already exists within the social media stream.
To get the best out of crowd sourced Twitter scoops, the best thing to do is create a group of varied, unconnected users, those with a solid record and ideally geographically close to an event. Look out for independent corroboration across different users, and be mindful that hundreds of re-Tweets rarely give more weight to the original Tweet that spawned it. Use other social media sources besides Twitter. And don't believe every Tweet you read - but don't discount them all either.