Methods
Sources of data
This study is based on the extensive analysis of six
comparable data sets from the BDHS carried out in 1993-94,
1996-97, 1999-2000, 2004, 2007 and 2011. Detailed
descriptions of the study designs, including informed consent
and data collection, were explained in the country-specific
reports [28]. All the Demographic and Health Surveys (DHS)
were nationally representative and employed a common
methodology across participating countries [29]. Many
developing countries of the world routinely conduct similar
surveys under the DHS programme. All these surveys were
financially and technically supported by the United States
Agency for International Development (USAID) [28]. The
authors received all the data sets from MEASURE DHS. The
DHS data collection procedures were ethically approved by the
ORC Macro (Calverton, Maryland) Institutional Review Board
[30]. Moreover, all these surveys were approved by the
relevant authority of the Ministry of Health and Family Welfare
in Bangladesh. A group of trained interviewers conducted faceto-
face interviews for data collection. Before starting each
interview, the interviewers also explained the objectives of the
survey and received informed consent from the respondents.