New research by the University of Michigan shows that you are more likely to pull out and use your mobile phone when someone around them does the same. Sort of like when you immediately yawn after someone else has; but whereas yawning is simply "contagious," this is a "contagious decision."
In 2011, this study was conducted by observing pairs of young people between 16 and 25, sitting at tables in dining halls and restaurants around campus. Mobile use was recorded in 10-second intervals to find out if one or both people checked their phone within this 10-second span.
Research found that in 36.5% of situations, the second person would reach for his or her phone when the first began using their own. A trend of "contagious" behaviour can be seen in this, along with the more "addictive" qualities of modern mobile phones. Individuals spent an average of 24% of the time with their friends, using their device.
According to the paper published in the Human Ethology Bulletin, researchers Julia A. Finkel and Daniel J. Kruger have identified two potential causes for this mobile use contagiousness. Either by prompting: the individual remembers to check for emails when his or her friend checks their own. Or by inclusion: a digital wall is put up between you and your friend, when said friend starts using their phone. In a mixture of requirement of interaction and social conformity, you will then usually pick up your phone and check Facebook, to ensure you're not just there staring into space.
Monkey see, Monkey do.