Spacing of children in Switzerland:

constancy or change?

Marion Burkimsher

Affiliated to

University of Lausanne

Change in mean age at birth of each birth order 1969-2007

25

26

27

28

29

30

31

32

33

34

35

36

37

19691970197119721973197419751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003200420052006200720082009Year

Age of mother

1st birth 2nd birth 3rd birth 4th birth 5th+ birth

Source BEVNAT

Birth spacing - what and why?

• Not difference in mean age of successive birth ordersNot difference in mean age of successive birth orders

• Can obtain spacing data from surveys (or census data), but not Can obtain spacing data from surveys (or census data), but not

birth registration by birth orderbirth registration by birth order

• Why these are different…(women who end up having bigger Why these are different…(women who end up having bigger

families start childbearing at a younger age; women who start later families start childbearing at a younger age; women who start later

have fewer children)have fewer children)

• With birth spacing data (probability of subsequent birth knowing With birth spacing data (probability of subsequent birth knowing

duration since last birth) - and female population by parity & age - duration since last birth) - and female population by parity & age -

can make good TFR projections by McDonald-Kippen methodcan make good TFR projections by McDonald-Kippen method

Differences in mean age at nth and (n+1)th birth

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

19691970197119721973197419751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003200420052006200720082009

Years

1st-2nd birth 2nd-3rd birth 3rd-4th birth

Source BEVNAT

Change in standard deviation of age at birth

3.8

4.0

4.2

4.4

4.6

4.8

5.0

5.2

5.4

19691970197119721973197419751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003200420052006200720082009Year

Standard deviation, years

Birth order 1 Birth order 2 Birth order 3 Birth order 4 Birth order 5+

Source BEVNAT

Example of erroneous deduction: spacing in SwitzerlandExample of erroneous deduction: spacing in Switzerland

FFS sample data from 1994 for women aged 40-44FFS sample data from 1994 for women aged 40-44

ie. cohorts 1950-1954ie. cohorts 1950-1954

Mean age at 1st birth 26.9Mean age at 1st birth 26.9

Mean spacing 1st-2nd child: 3.13 yearsMean spacing 1st-2nd child: 3.13 years

Mean spacing 2nd-3rd child: 3.62 yearsMean spacing 2nd-3rd child: 3.62 years

Mean spacing 3rd-4th child: 3.13 yearsMean spacing 3rd-4th child: 3.13 years

Houle & Shkolnikov, 2006 then made the following Houle & Shkolnikov, 2006 then made the following incorrectincorrect deductions using age at 1st birth as the starting point:deductions using age at 1st birth as the starting point:

Deduced mean age at 2nd birth 30.0Deduced mean age at 2nd birth 30.0

Deduced mean age at 3rd birth 33.6Deduced mean age at 3rd birth 33.6

Deduced mean age at 4th birth 36.8Deduced mean age at 4th birth 36.8

RestatingRestating……

We cannot deduce anything about birth spacing from differences We cannot deduce anything about birth spacing from differences in mean age at successive birth orders!in mean age at successive birth orders!

We cannot deduce anything about mean age of successive birth We cannot deduce anything about mean age of successive birth orders from information on birth spacing!orders from information on birth spacing!

Why?Why?

Because women who have their first child at a younger age have Because women who have their first child at a younger age have more likelihood of having a larger family than women who start at more likelihood of having a larger family than women who start at a later age.a later age.

This is easier to understand with an illustration…This is easier to understand with an illustration…

2 hypothetical scenarios…

2525 2828 3131 3434

Mean age at 1st birth: 25Mean age at 1st birth: 25Mean age at 2nd birth: 28Mean age at 2nd birth: 28Mean age at 3rd birth: 31Mean age at 3rd birth: 31Mean age at 4th birth: 34Mean age at 4th birth: 34

Mean spacing between all Mean spacing between all birth orders: 3 yearsbirth orders: 3 years

Mean age at last birth: Mean age at last birth: 29.529.5

AgeAge

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Scenario 1: Scenario 1: 4 women, having 1, 2, 3 and 4 children respectively4 women, having 1, 2, 3 and 4 children respectively

2525 2828 3131 3434

Mean age at 1st birth: 29.5Mean age at 1st birth: 29.5Mean age at 2nd birth: 31Mean age at 2nd birth: 31Mean age at 3rd birth: 32.5Mean age at 3rd birth: 32.5Mean age at 4th birth: 34Mean age at 4th birth: 34

Mean spacing between all Mean spacing between all birth orders: 3 yearsbirth orders: 3 years

Mean age at last birth: 34Mean age at last birth: 34

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AgeAge

Scenario 2: Scenario 2: 4 women, having 1, 2, 3 and 4 children respectively4 women, having 1, 2, 3 and 4 children respectively

Hypothesis

That between 1969 and the present time there has been a

transition from Scenario 1 being the norm to Scenario 2.

But we need birth spacing data…

Using data from SHP

• Data about cohabiting children had to be combined with data on (older) children who had moved out of the household

• Frequency curves of spacing are skewed; modal gap < median gap < mean gap

• Likelihood of going on to a 2nd / 3rd child changes over time

• Solution - survival analysis, life table method (as only whole year data)

• Survival analysis gives:

1. change in intensity

2. change in ultimate likelihood

3. median duration of transition (if >50% experience it)

Interesting statistics from SHP sample

Longest gap 1st-2nd for a woman is 18 years

Longest gap 1st-2nd for a man is 32 years

Longest gap 2nd-3rd for a woman is 31 years!

Longest gap 2nd-3rd for a man is 25 years

Range, age at 1st birth, woman - 15-54 years

Range, age at 1st birth, man - 12-59 years

Range, age at 2nd birth, woman - 17-49 years

Range, age at 2nd birth, man - 16-59 years

…as men have no upper bound, only look at women’s rates …

Frequency curve for 2nd child after 1stand 3rd child after 2nd by duration

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0 1 2 3 4 5 6 7 8 9

Number of years after 1st/2nd child

Probability of 2nd/3rd birth

1960s 2nd child

1970s 2nd child

1980s 2nd child

1990s 2nd child

1960s 3rd child

1970s 3rd child

1980s 3rd child

1990s 3rd child

Modal gap 1st-2nd & 2nd-3rd is

2 years

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Median gap

% no 2nd

1960s 3.3 20

1970s 3.5 18

1980s 3.3 17

1990s 3.3 18

2000> 3.6 22

No significant change in

1st-2nd gap from 1960s to present day!

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But significant changes for 2nd-3rd child

transition!

How does age of mother affect spacing?

…remembering that age at childbearing has been rising over time

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Significantly less likelihood

of women having a 2nd

child if over 35 when 1st born

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Very significant difference in likelihood of

woman having 3rd child if her

2nd born before/after 30

Various potential determinants 1st-2nd likelihood 2nd-3rd likelihood Decade of birth of 1st/2nd child

Yes, >2000 s lightly lower Yes, 1960s higher intensity

Age of mother at bi rth of 1st/2nd

Yes, older mothers lower Yes, older mothers lower

Religious attendance Yes, regular attenders higher

Yes, very signif. diffs.

Education level (3 groups) Not significant Yes, low ed., higher intensity

Gender of 1st child Not significant - Linguistic areas Slight

German>French>Italian German>French>Italian

1st 2 children twins - Yes, higher if twins Mother born in CH Slight, higher if born in

CH Yes, higher if born in CH

Cannot yet confirm or deny hypothesis

Initial investigations encouraging…

SHP is only up-to-date data source on birth spacing in

Switzerland

More work to be done…

Spacing of children in Switzerland:

constancy or change?

• 1st-2nd child transition > constancy

• 2nd-3rd child transition > change (decline in likelihood)

Thank you!