Received: 30 August 2018
Revised: 18 February 2019
Accepted: 5 March 2019
First Online: 24 April 2019
Compliance with ethical standards
: The authors declare that they have no conflict of interest.
: The views expressed in this article are those of the author(s) and do not reflect the official policy of the Department of the Army/Navy/Air Force, Department of Defense, or the U.S. Government.