Funding for this research was provided by:
EEA Grants Program, Public Health Initiatives. (PT06 - 000088SI3)
Received: 22 March 2018
Accepted: 18 December 2019
First Online: 2 January 2020
Compliance with ethical standards
: Ethical approval was obtained from the National Commission for Data Protection, the Ethical Committee of the Institute of Public Health of the University of Porto and from the Ethical Commissions of each one of the Regional Administrations of Health. All participants were asked to provide their written informed consent according to the Ethical Principles for Medical Research involving human subjects expressed in the Declaration of Helsinki and the national legislation.
: The authors declare that there are no conflicts of interest.