Received: 17 November 2017
Accepted: 22 February 2018
First Online: 2 March 2018
Ethics approval and consent to participate
: As a register-based blinded analysis, the study did not have identifiable individual participants and thus neither informed consent nor ethics approval was needed according to Finnish legislation (medical research act 488/1999, amendments 295/2004, 794/2010).
: Not applicable.
: Teemu Hevonkorpi, Antti Launonen, Tuomas Huttunen, Pekka Kannus, Seppo Niemi and Ville Mattila declare that they have no conflicts of interest.
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