Spacing of children in Switzerland: constancy or change? Marion Burkimsher Affiliated to University of Lausanne

Source BEVNAT

Birth spacing - what and why? Not difference in mean age of successive birth orders Not difference in mean age of successive birth orders Can obtain spacing data from surveys (or census data), but not birth registration by birth order Can obtain spacing data from surveys (or census data), but not birth registration by birth order Why these are different…(women who end up having bigger families start childbearing at a younger age; women who start later have fewer children) Why these are different…(women who end up having bigger families start childbearing at a younger age; women who start later have fewer children) With birth spacing data (probability of subsequent birth knowing duration since last birth) - and female population by parity & age - can make good TFR projections by McDonald-Kippen method With birth spacing data (probability of subsequent birth knowing duration since last birth) - and female population by parity & age - can make good TFR projections by McDonald-Kippen method

Source BEVNAT

Example of erroneous deduction: spacing in Switzerland FFS sample data from 1994 for women aged ie. cohorts Mean age at 1st birth 26.9 Mean spacing 1st-2nd child: 3.13 years Mean spacing 2nd-3rd child: 3.62 years Mean spacing 3rd-4th child: 3.13 years Houle & Shkolnikov, 2006 then made the following incorrect deductions using age at 1st birth as the starting point: Deduced mean age at 2nd birth 30.0 Deduced mean age at 3rd birth 33.6 Deduced mean age at 4th birth 36.8

Restating … We cannot deduce anything about birth spacing from differences in mean age at successive birth orders! We cannot deduce anything about mean age of successive birth orders from information on birth spacing! Why? Because women who have their first child at a younger age have more likelihood of having a larger family than women who start at a later age. This is easier to understand with an illustration…

2 hypothetical scenarios…

Mean age at 1st birth: 25 Mean age at 2nd birth: 28 Mean age at 3rd birth: 31 Mean age at 4th birth: 34 Mean spacing between all birth orders: 3 years Mean age at last birth: 29.5 Age Scenario 1: 4 women, having 1, 2, 3 and 4 children respectively

Mean age at 1st birth: 29.5 Mean age at 2nd birth: 31 Mean age at 3rd birth: 32.5 Mean age at 4th birth: 34 Mean spacing between all birth orders: 3 years Mean age at last birth: 34 Age Scenario 2: 4 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 years Range, age at 1st birth, man years Range, age at 2nd birth, woman years Range, age at 2nd birth, man years …as men have no upper bound, only look at women’s rates …

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

Median gap % no 2nd 1960s s s s >3.622 No significant change in 1st-2nd gap from 1960s to present day!

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

Significantly less likelihood of women having a 2nd child if over 35 when 1st born

Very significant difference in likelihood of woman having 3rd child if her 2nd born before/after 30

Various potential determinants

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!