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Article History

Received: 6 March 2017

Accepted: 9 March 2018

First Online: 12 April 2018

Ethics approval and consent to participate

: This study did not involve human participants or animal participants. Sensible data from public registers are anonymous and we used such data under the permission of the National Institute of Social Security. We used data from public registers in accordance with the Italian and European laws and regulations on privacy and sensible data.

: Not applicable.

: The authors declare that they have no competing interests.

: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.