Article History
First Online: 18 September 2019
Compliance with Ethical Standards
:
: No sources of funding were used to conduct this study or prepare this manuscript.
: Søren Kabell Nissen, Anton Pottegård, and Jesper Ryg have no conflicts of interest that are directly relevant to the content of this study.
: This study was based on aggregate data, and no ethical approval was necessary.
: All data generated or analysed during this study are included in the paper or its supplementary files.