The study was approved by the Danish Data Protection Agency (No. 1-16-02-40-17) and by the Danish National Board of Health (No. 3-3013-2049/1).
According to the Act on Research Ethics Review of Health Research Projects, register-based studies do not require an approval from the research ethics committee system (No. 1-10-72-4-17).
Copyright and License information: The Author(s). ©2019 Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
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