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Population

Development of births

Average number of children

The development of births is one of the central factors of demographic change in Germany. Therefore, measures of births receive considerable attention from society. Official statistics provide manifold basic information on births and the fertility behaviour of women. An overview is provided in the brochure "Geburten in Deutschland - 2012 edition".
The present article explains a measure which is quoted very often: the "average number of children per woman". Generally, this indicator is used to make fertility comparable while disregarding the age structure of women. In order to use and interpret this benchmark figure correctly, which seems rather simple at first glance, we need to distinguish between the fertility of women in a given calendar year and the lifetime fertility of women belonging to a specific birth cohort.

The total fertility rate of the calendar years

Every year, the official statistical agencies publish the current birth rate, which is the total fertility rate of a calendar year. It is a current benchmark figure characterising the fertility behaviour of women in the respective calendar year. The fertility behaviour is measured by means of the age-specific fertility rates calculated for each individual age year between 15 and 49. The age-specific fertility rate shows the relationship between the number of children born by mothers of a certain age and the number of all women of that age. Adding up – and thus aggregating – the age-specific fertility rates yields the total fertility rate.

What does the following statement mean: "in 2012, the total fertility rate was 1.38 children per woman"?

The above total fertility rate shows the fertility of all women aged 15 to 49 years in 2012. Assuming that these women form a hypothetical cohort, the final number of children born on average to that cohort would be 1.38 children per woman.
Due to its hypothetical nature, the total fertility rate of the calendar years is suitable only to a limited extent for properly assessing the average number of children finally born to a real female cohort. For this purpose, the final number of children or cohort fertility should be used.

What is the informational value of the total fertility rate?

To maintain the present number of the population, more than 2 children would have to be born per parental couple (total fertility rate of 2.1 children per woman), who, in turn, would have to have at least 2 children when they are grown up to replace the previous generation. A birth rate below this replacement level, as it is called, leads to a shrinking und ageing population.

What does an increase or decrease of the total fertility rate imply?

When the total fertility rate goes up or down, this means in the first place that the age-specific fertility rates have changed. This may be a short-lived reaction to economic, social or political stimuli or it may be due to a changing fertility behaviour. To distinguish short-term fluctuations from a trend, the age-specific fertility rate should always be considered in connection with the development of age-specific fertility and cohort fertility. This is the more important as even a constant total fertility rate is no clear indication of stable fertility behaviour. A good example is the development recorded over the last few decades: while the total fertility rate varied only slightly at around 1.4 children per woman, the fertility rates of women below the age of 30 fell persistently and the fertility rates of those over 30 years went up. On the whole, these effects compensated each other and influenced the total fertility rate only marginally.

How did the total fertility rate change between 1950 and 2012?

At the beginning of the 1960s, the two parts of Germany had seen an increase in births, represented by the highest total fertility rates of the post-war period (2.5 children per woman). The children born in that period are today’s large cohorts of the mid-forties. The subsequent sharp fall in the number of births started as early as in 1964 in the former GDR, and since 1967 the number of births decreased continuously also in the former territory of the Federal Republic. Consequently, the total fertility rate decreased strongly, too.

Enlarge picture

The decline in the former territory of the Federal Republic lasted for nearly twenty years and in the mid-1980s the total fertility rate reached its all-time low with fewer than 1.3 children per woman. The decrease in the total fertility rate was caused not only by the fact that fewer children were actually born than in the previous years. The decline in fertility was also due to the fact that an ever larger share of the women postponed starting a family to an older age. Then the total fertility rate rose to 1.45 in 1990 before fluctuating slightly around 1.4 children per woman (except for individual years).
The former GDR counteracted the declining birth rate from the mid-1970s by comprehensive government support for families with children. That policy actually resulted in a short-term increase in the total fertility rate to 1.94 children per woman in 1980. Then fertility gradually decreased there, too. As a consequence of the radical economic and social changes occurring in the new Länder in the context of German unification, the number of births and thus the total fertility rate fell sharply there: from 1990 to 1994 the total fertility rate was down from 1.52 to 0.77. Since 1995 the fertility of women in the new Länder thus measured has been growing again. In 2007 it reached the level of the old Länder (1.37 children per woman) and from 2008 it was even higher at 1.40.
For 2012, birth statistics show a slight increase of the total fertility rate for Germany from 1.36 to 1.38 children per woman. This is about the level of 2008. In the new Länder the total fertility rate (1.45 children per woman) was higher than in the former territory of the Federal Republic (1.37).

Cohort fertility (final number of children)

The average number of children per woman is calculated also as a measure of the cohort fertility of female cohorts. When the age-specific fertility rates are added up, this is not done for a specific calendar year. Instead, the age-specific birth rates of the 35 calendar years are used in which the women of a cohort were 15 to 49 years old. Once a cohort has reached the age of 50, the total fertility rate thus calculated corresponds to the final average number of children born to that cohort. In 2012 this was the 1963 cohort; the women of that cohort gave birth to an average 1.6 children.
In the case of younger women a possible alternative is using the average number of children born until the relevant age (calculated as the sum of the age-specific birth rates until that age). It may be helpful, for instance, to compare the number of children which the 1950 and 1970 cohorts gave birth to until they turned 35. The final number of children born to women under 49 years of age, however, can only be estimated. Estimates are reliable for the cohorts aged 43 to 48 years as the final number of children changes only marginally from the age of 43. For the time being it remains unknown how many children younger women will give birth to later.

What is the difference between the total fertility rate of a year and the final number of children born to a cohort?

The final number of children born to a cohort differs from the total fertility rate of a calendar year in terms of the underlying concept and mostly also the level. The total fertility rate of a calendar year represents the average number of children resulting from the fertility behaviour of women in a given year. Births that occurred before and after the year in question are not taken into consideration. In contrast, the final number of children reflects the specific behaviour pattern of real female cohorts with regard to family formation. Most women of the older cohorts gave birth to their children at an earlier point in their lives than the women of younger generations. During the transition to the new fertility behaviour, which was first shown by the decrease in the fertility of the under 30 year olds, the total fertility rate of the calendar years fell sharply (chart "Total fertility rate of the calendar years"): late 1960s to early 1970s in the former territory of the Federal Republic, early 1990s in the new Länder. As starting a family late in life does not necessarily mean fewer children, many women "caught up” by giving birth to children at an older age. The increasing age of women giving birth for the first time in fact led to a decreasing final number of children for the women of the cohorts concerned. However, that decrease was not as serious as was at first expected in view of the decrease observed for the total fertility rate of the calendar years.

How has the cohort fertility of the female cohorts developed?

There are differences between the female cohorts in the former territory of the Federal Republic on the one hand and the new Länder on the other, both in the current level and the development of fertility to date (chart "Total fertility rate of the female cohorts"). In both parts of Germany, the women born in the 1930s gave birth to about the same average number of children: the final number of children born to women of these cohorts was over 2 children per woman. In the following thirty years, the final number of children per woman was down by about 25% in the former territory of the Federal Republic. The decrease was particularly sharp for the cohorts from 1934 (2.2) to 1943 (1.8). That decline reflected the transition from the highly family-oriented fertility behaviour in the baby boom period (late 1950s to mid-1960s) to new ways of life which emerged as a result of social change in the late 1960s and early 1970s. Afterwards, the decrease continued at a slower pace. The women of the 1963 cohort, who reached the age of 50 in 2012, gave birth to an average 1.6 children in the former territory of the Federal Republic.
In the former GDR the final number of children of the female cohorts decreased from 2.1 to 1.8 children per woman for the 1934 to 1947 cohorts, which is similar to western Germany, but it then remained at this relatively high level for more than a decade. As is shown in the chart "Total fertility rate of the calendar years", the annual total fertility rate also decreased considerably in the former GDR in the early 1970s. However, the decline of births did not last long there: from as early as 1976, the total fertility rate of the calendar years increased again. The final number of children of the female cohorts was not affected by that brief decrease.

Number of children per woman, by birth cohortEnlarge picture

The 1960 cohort marked a new trend in the cohort fertility of women in eastern Germany. The final number of children born to the 1960 and 1961 cohorts declined as compared to the 1950s cohorts.
In the five years to come, the final number of children per woman is expected to go down further. The women born in 1968, for instance, have given birth to an average 1.5 children until they turned 44. Their final number of children at the age of 49 will quite probably be lower than that of the women born in 1963 (1.6).

See also the methodological notes on "birth rates and tempo effect", the brochure entitled "Geburten in Deutschland – 2012 edition", our StatMagazin "Low birth rates and not enough mothers …".

© Statistisches Bundesamt (Destatis), 2018

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