Received: 29 August 2019
Accepted: 30 March 2020
First Online: 10 April 2020
Ethics approval and consent to participate
: This systematic review is part of a bigger research project. Ethical approval for the project was obtained from the Research Ethics Committee of the Faculty of Health Sciences, University of Pretoria (ethics reference number: 146/2016)
: Not applicable.
: The authors declare that they have no competing interests.