Received: 30 October 2018
Accepted: 20 August 2019
First Online: 30 August 2019
Ethics approval and consent to participate
: The research protocol was approved by the Ethical Review Committee of the School of Public Health at Tehran University of Medical Sciences. The study was based on secondary data and did not involve data collection at individual level or human subjects.
: Not applicable.
: The authors declare that they have no competing interests.