Received: 25 October 2018
Accepted: 7 February 2019
First Online: 14 February 2019
Ethics approval and consent to participate
: Not applicable; in this study we analyzed only published literature.
: Not applicable
: Livia Puljak is a member of the editorial board (Section Editor) of the BMC Medical Research Methodology.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.