- Correspondence to Dr Raina M Merchant, Penn Medicine Social Media and Health Innovation Lab, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA;
- Received 3 February 2015
- Revised 15 June 2015
- Accepted 4 July 2015
- Published in print 1 January 2016.
- Published online 15 December 2015.
- Published first 24 July 2015.
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- Data supplement 1 - Online supplement
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