VID Colloquium
Increasing Child lessness or few er Fam ilies
w ith m any Child ren - A Decom position
Method for Changes betw een (Cohort)
Fertility Rates
Martin Bu jard ,
Fed eral Institute for Popu lation Research (BiB), Wiesbad en, Germany
Date: Thu , 21 May 2015, Time: 11:00 - 12:00 am
The d ecline of fertility in the course of the Second Dem ographic Transition is m a inly
caused by both an increase in child lessness and a d ecline of large fam ilies (three or
m ore child ren). Ad d itionally, in som e countries the spread of one parent fam ilies
red uced fertility rates. Each of these three phenom enons has d ifferent causes and
need s to be explained by d ifferent theories. Their contribu tion to fertility changes
varies betw een d ifferent countries and regions. An exact quantification of the
contribu tion of each of these effects to fertility changes is still m issing. Existing
d elim itation often is d ualistic; it only d istinguishes betw een child lessness and the
average num ber of child ren per m other. I suggest a d ecom position m ethod w hich
allow s calculating the effects of the particular parity changes betw een cohort total
fertility rates (CTFR) of d ifferent cohorts. The CFR d ecline can be separated into four
com ponents: increasing child lessness, d ecreasing shares of higher ord er births (3+),
an interaction effect and a changing relation of first and second births. This m ethod is
applied in ord er to com pare Germ an CTFRs betw een 1933 and 1970 based on Micro
Census d ata of 2008 and 2012. The analyses are d ifferentiated by regions, period s and
ed ucational groups. The effect of the increasing child lessness accounts for 27.1 per
cent of the CFR d ecline, the d ecreasing higher ord er births for 66.6 per cent and the
interaction effect for 6.3 per cent. Germ any turns out to be a special case because the
relation of parity 1 and 2 has not changed . Rem arkably, these figures are based on
tw o entirely d ifferent period s: The CFR d ecline betw een the cohorts of 1933 and 1947
is solely based on the d ecline of fam ilies w ith three or m ore child ren. H ow ever, tw o
third s of the CFR d ecline betw een 1947 and 1970 is caused by an increasing
child lessness. Differentiated by ed ucational groups, the contribution of increasing
child lessness begun earlier in is stronger for low ed ucated w om en. The
d ecom position m ethod is suitable for the analysis of d ynam ics end ing in low fertility.
Its application for an international com parison of CTFR-d ecline and for ad justed TFR
m easures is still to be tested but seem s prom ising.
About the presenter
Martin Bujard is research d irector of the grou p “Fam ily and Fertility” at the Fed eral
Institute for Population Research (BiB), Wiesbad en, Germ any. H e hold s a PhD from
the Ruprecht-Karls-University H eid elberg, Faculty of Econom ics and Social Sciences.
Before w orking in the sciences, he w as m anager of a catalogue selling business and
scientific assistant at the Germ an Fed eral Parliam ent in Ber lin. 2009 until 2011 he
w orked at the H um bold t University as scientific coord inator in the Group »Futu re
w ith Child ren« established at Leopold ina and BBAW. Since August 2011 he w orks at
the BiB. H is research lies in the intersection betw een d em ography, fam ily policy, and
fam ily sociology. Research field s are parental leave, d eterm inants of fertility in OECD
countries, child lessness and large fam ilies.
© VID