Table 1 Random-effects logistic regression of factors associated with poory spaced inter-birth intervals (<33 months) in Rufiji, Tanzania: 1999–2010 (n = 15,158)

Maternal age (years)

 15-19

13.65

9.63-19.35

<0.001

 20-24

4.30

3.16-5.86

<0.001

 25-29

2.40

1.77-3.26

<0.001

 30-34

2.07

1.52-2.80

<0.001

 35-39

1.64

1.21-2.24

0.002

 40-44

1.31

0.95-1.83

0.100

 45-49 (ref.)

1.00

––

––

Marital status of mother

 Married (ref.)

1.00

––

––

 Ever married (widowed or divorced)

0.56

0.48-0.66

<0.001

 Single

0.64

0.57-0.73

<0.001

Maternal education

 Secondary/higher (ref.)

1.00

––

––

 Primary

1.09

0.87-1.37

0.456

 Never been to school

1.27

1.01-1.60

0.042

Place of residence

 Urban (ref.)

1.00

––

––

 Rural

1.04

0.95-1.13

0.400

Parity

 2 (ref.)

1.00

––

––

 3

1.29

1.19-1.40

<0.001

 ≥4

2.54

2.28-2.85

<0.001

Birth

 Singleton (ref.)

1.00

––

––

 Multiple

0.74

0.57-0.96

0.023

Place of delivery of the index child

 Health facility (ref.)

1.00

––

––

 Elsewhere

1.85

1.71-2.00

<0.001

HDSS entry type

 Enumeration (ref.)

1.00

––

––

 In-migration

1.32

1.21-1.45

<0.001