Funding for this research was provided by:
Received: 2 August 2017
Accepted: 28 May 2018
First Online: 13 June 2018
Ethics approval and consent to participate
: The data linkage in this study was approved by the Danish Data Protection Agency (Ref.GEH-2014-014). All data were linked and stored in computers held by Statistics Denmark which ensured anonymity. According to the Act on Processing of Personal Data, register-based studies with no human biological material do not require ethical approval [CitationRef removed].
: The authors declare that they have no competing interests.
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