Table 4 Factors associated with time to second birth interval among women in Nigeria and South Africa

Fertility desired

No more (R)

1

1

1

1

1

1

Wanted

1.02(0.99,1.05)

1.02(0.99,1.05)

1.00(0.97,1.03)

0.50(0.46,0.54)^c

0.51(0.47,0.55)^c

0.51(0.47,0.55)^c

Undecided

1.07(1.01,1.12)^a

1.07(1.01,1.12)^a

1.03(0.98,1.08)

0.73(0.62,0.84)^c

0.76(0.65,0.88)^c

0.74(0.64,0.86)^c

Contraceptive use

Never

0.97(0.93,1.00)

0.96(0.93,1.00)^a

0.80(0.77,0.83)^c

0.75(0.69,0.81)^c

0.77(0.71,0.83)^c

0.76(0.70,0.82)^c

Formal

0.88(0.84,0.92)^c

0.88(0.84,0.92)^c

0.84(0.81,0.88)^c

0.85(0.79,0.92)^c

0.91(0.84,0.98)^a

0.90(0.83,0.97)^b

Current (R)

1

1

1

1

1

1

Ethnicity

Hausa (R)

1

1

Igbo

0.78(0.75,0.81)^c

1.06(1.00,1.13)^a

Yoruba

0.62(0.60,0.65)^c

0.77(0.73,0.81)^c

Don’t know/others

0.73(0.71,0.75)^c

0.89(0.85,0.92)^c

Black/African (R)

1

1

White

1.45(1.19,1.76)^c

1.53(1.24,1.88)^c

Coloured

0.99(0.89,1.10)

1.05(0.94,1.17)

Indian/Asian/other

1.00(0.74,1.36)

1.09(0.80,1.49)

Residence

Urban (R)

1

1

1

1

Rural

1.16(1.13,1.19)^c

1.05(1.02,1.09)^b

1.27(1.19,1.35)^c

1.16(1.07,1.24)^c

Religion

Christianity (R)

1

1

Islam

1.37(1.33,1.40)^c

1.22(1.17,1.27)^c

Traditionalist/other

1.17(1.03,1.34)^a

1.31(1.14,1.49)^c

Age at FB

 < 20 (R)

1

1

1

1

20–24

0.92(0.89,0.95)^c

1.02(0.99,1.05)

0.99(0.92,1.06)

1.02(0.96,1.10)

 ≥ 25

0.83(0.80,0.87)^c

0.98(0.94,1.02)

0.80(0.72,0.88)^c

0.88(0.79,0.98)^a

Wealth index

Low (R)

1

1

1

1

Middle

0.86(0.83,0.88)^c

0.95(0.92,0.98)^b

0.87(0.81,0.94)^c

0.92(0.86,1.00)^a

High

0.73(0.71,0.75)^c

0.87(0.83,0.90)^c

0.71(0.66,0.77)^c

0.75(0.68,0.83)^c

Education

No education (R)

1

1

1

1

Primary

0.81(0.79,0.84)^c

0.97(0.93,1.01)

0.97(0.81,1.17)

0.96(0.79,1.15)

Secondary

0.75(0.73,0.77)^c

0.99(0.95,1.03)

0.74(0.63,0.88)^b

0.86(0.72,1.02)

Higher

0.69(0.66,0.72)^c

0.93(0.87,0.99)^a

0.67(0.55,0.81)^c

0.88(0.71,1.08)

Employment

Not working (R)

1

1

1

1

Working

0.85(0.82,0.87) ^c

0.95(0.92,0.98)^b

0.85(0.79,0.90)^c

0.85(0.79,0.90)^c

Marital at FB

Never married (R)

1

1

1

1

Married before FB

3.67(3.27,4.12)^c

3.26(2.90,3.66)^c

1.63(1.51,1.77)^c

1.57(1.45,1.70)^c

Married after FB

3.02(2.68,3.41)^c

2.87(2.55,3.24)^c

1.30(1.21,1.39)^c

1.32(1.23,1.42)^c

FB sex

Male (R)

1

1

Female

1.00(0.97,1.02)

1.00(0.94,1.07)

FB survival

Dead

1.13(1.07,1.19)^c

1.11(1.05,1.16)^c

0.94(0.80,1.11)

Alive (R)

1

1

1

Deviance (-2ll)

458,619.0^c

456,902.2^c

62,423.8^c

62,116.4^c