Text and Data Mining valid from 2018-05-09
Received: 13 June 2017
Accepted: 24 April 2018
First Online: 9 May 2018
Ethics approval and consent to participate
: Ethical approval for this study was not required as the data were available for use upon approval. We obtained permission to use the data from the ICF International, Rockville, Maryland, USA in May 2017.
: The authors declare that they have no competing interests.
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