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Porn, smart phones and the \\u2018slutty transmitter\\u2019. Adults in the US have sex on average about 50 times a year, which has dropped by 20 per cent over the last two decades. It\\u2019s a similar story in the UK, Australia, Germany, Finland and Japan. Could it be down to porn or our smart phones? Or is it actually down to something much harder to switch off? Some of the answers might surprise you.

Picture: A couple in bed using their phones. Credit: Getty Images