Received: 16 January 2018
Accepted: 18 October 2018
First Online: 29 October 2018
: SSA is a Reader, BLS is a Senior Lecturer, OOB is a Lecturer 1 while BOO is a Doctoral Student in the Department of Demography and Social Statistics, Obafemi Awolowo University, Ile-Ife, Nigeria.
: The surveys were approved by the National Health Research Ethics Committee (NHREC/01/01/2007). Informed consent was obtained from participants in the 2003, 2008 and 2013 NDHS. Authorisation to download and analyse the dataset was granted by MEASURE DHS.
: Not Applicable.
: The authors declare that they have no competing interests.
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