Text and Data Mining valid from 2018-04-12
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.
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