Footnotes

• Contributors AB, JFL and AS wrote the first draft of the paper. AB and AS performed the statistics.

• Funding This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

• Patient consent Not required.

• Ethics approval Stockholm Ethics Review Board, Sweden.

• Provenance and peer review Not commissioned; internally peer reviewed.

• Data sharing statement Data can be obtained from the National Board of Health and Welfare in Sweden.