Definition of explanatory variables used in the analysis
| Variables | Definition and coding |
| Year | 2003/2008/2013 |
| Age group of respondents | 1=15–19; 2=20–24; 3=25–29; 4=30–34; 5=35–39; 6=40–44; 7=45–49 |
| Type of place of residence | 1=Urban; 2=Rural |
| Geographical region | 1=North Central; 2=North East; 3=North West; 4=South East; 5=South South; 6=South West |
| Education | 0=None; 1=Primary; 2=Secondary; 3=Tertiary |
| Religion | 1=Christianity; 2=Islam; 3=Other religion/none |
| Employment | 0=Unemployed; 1=Employed |
| Sex of household head | 1=Male; 2=Female |
| Household wealth status* | 1=Poorest; 2=Poorer; 3=Middle; 4=Richer; 5=Richest |
| Total children ever born | 1=1–2; 2=3–4; 3=>4 |
| Modern contraceptive use | 0=No; 1=Yes |
| Domestic violence | 0=No; 1=Yes |
| Intimate partner violence | 0=No; 1=Yes |
| Marital status | 1=currently married/living with a partner; 2=Not currently married |
↵*For the calculation household wealth status, instead of direct income, the volume of durable goods (eg, TV, radio, bicycle) possessed by the household as well as and housing quality (eg, type of floor, wall and roof) are taken into consideration. Each item is assigned a factor score generated through principal component analysis which are then summed and standardised for the households. These standardised scores places the households in a continuous scale based on relative wealth scores. The scores thus obtained from a continuous scale and subsequently categorised into quintiles to rank the household as poorest/poorer/middle/richer/richest to richest.22 For the present study, households in lowest two categories were merged and categorised as poor, and those from middle to richest were merged as non-poor.