Table 1 Description of explanatory variables

Year of survey

Survey years classified into 4 groups 2003; 2008, 2013 and 2018.

Age group

Age group of respondents at the time of the survey classified into 2 groups: 15–19 and 20–24 years

Education

Education attainment of the women classified into 3 groups: no education, primary; secondary and above

Marital status

Classified into 4 groups: never married; currently married; living with a partner (but not legally married) and previously married (widowed, divorced, separated).

Wealth index

Constructed by the DHS using principal components analysis based on household assets. Classified into five groups: Poorest; Poorer; Middle; Richer and Richest.

Contraceptive use

Denotes percentage of women in a cluster/state who currently use contraceptive methods. At individual level, this is a dichotomous variable classified as users and nonusers

Age at first sex

Classified into 2: Never had sex; Less than age 15; 15–17 and 18+ years

Forced sex

Ever forced to perform unwanted sexual acts. Classified into 2 groups: Yes and No

Frequency of reading newspaper

Classified into 3 groups: Not at all; Less than once a week and at least once a week or more.

Frequency of listening to radio

Classified into 3 groups: Not at all; Less than once a week and at least once a week or more.

Frequency of watching TV

Classified into 3 groups: Not at all; Less than once a week and at least once a week or more.

No of living children

Number of living children at the time of the interview. Classified into 4 groups; 0, 1, 2 and 3⁺

Ethnicity

Ethnic origin of respondents classified into 4 groups: Hausa; Igbo; Yoruba and Others

Religion

Religious affiliation of respondents, classified into 3 groups: Catholic; other Christians and Islam.

Place of Residence

Place of residence, grouped into 2: Urban and rural

Region

Region of residence grouped into 6: North Central, North East; North West; South East; South South; South West.