Conflict of interest
No conflict of interest has been declared by the authors.
Author contributions
SSR was responsible for the study conception and design.
SSR and KM performed the data collection. SSR and THR
performed the data analysis. SSR, KM and KMD were
responsible for the drafting of the manuscript. KMD made
critical revisions to the paper for important intellectual
content. THR provided statistical expertise. SSR obtained
funding. SSR and KMD provided administrative, technical
or material support. KM, KMD and THR supervised the
study