In 1948 Harold Lasswell defined the objective of media communications research as discovering “who says what to whom in what channel with what effect”. The difficulty for researchers has been that for the first half-century or so after Lasswell set out the aim, it has been largely impossible.

Perhaps that is now changing. Online social networks generate a huge amount of information about who says what to whom. Economists, computer scientists and sociologists are now digging through these social networks for the answers to long-standing questions – and few answers are as eagerly awaited as the secret of producing a sure-fire hit.

So how do you produce the perfect film or write the perfect book – or compose the perfect tweet on Twitter – in a way that will maximise the chances of catching on? Duncan Watts, a mathematical sociologist at Columbia University and Yahoo! Research, has answers – and I’m afraid they’re not too encouraging. “I’ve been using social media to promote my book,” he says, “and it’s just a waste of time – it has almost no impact at all.”