title: Feasibility of Conducting Retrospective Studies Using Hashtags and Social Media Data From Facebook and Twitter.
authors.affiliation: Hashtago, Kiev, Ukraine.
authors.forename: A
authors.initials: A
authors.lastname: Volovyk
authors.affiliation: Digital Health Outcomes, Brussels, Belgium.
authors.forename: O
authors.initials: O
authors.lastname: Topachevskyi