Topic outline

  • 203 HUMAN REPRODUCTION

    To go back to the previous course, click the title here 202 Ratios & Population Composition
    • 203.1 Reproduction & Demography


      A few words are warranted on the terminology used in Demography relating to births.

      The term "Fertility" is used in a different way to other contexts. For example when referring to soil in agriculture we might say soil is fertile, meaning it has the potential to growth things even though nothing is growing there at present.  Similarly you might expect that saying a woman or man is fertile might imply they are capable of achieving conception of a baby but this is not how the term is used in Demography.

      In Demography, the term "Fertility" is applied to a Rate of Birth and measures the number of live births occurring to women during a particular time period.  Stillborn babies are not counted in calculating Fertility or Birth rates. Although it is much less common, some demographic research examines Fertility rates relative to the father's age rather than the mother's age.  In this case it would be referred to as a study of Male Fertility. 

      Another term used in Demography relating to reproduction is "Childlessness". This refers to the number of women who have passed through childbearing ages without giving birth to any live babies.

      The following 2 page document gives a detailed description of a number of terms used in Demography and Epidemiology relating to child birth statistics.

      • 203.2 Total Fertility Rate

        There are a number of different birth rates, fertility rates and rates of reproduction which Demographers use. 

        In this Course you will mainly focus on the Total Fertility Rate.  The Total Fertility Rate (TFR) is the average number of children that would be born alive to a woman (or group of women) during her lifetime if she were to pass through her childbearing years conforming to the age-specific fertility rates of a given year for each age 15 to 49 (the reproductive age range).
        When you read articles discussing fertility rates around the world, it is most likely they will be quoting Total Fertility Rate. You might have to look at footnotes and other references to confirm this. Tables are often headed "Fertility Rate" without the full technical title and may not mention whether it is quoted per 100 women or per woman. Below is an illustration of this taken from the initial summary page of the Australian Bureau of Statistics publication 3301.0 - Births, Australia, 2016. We have highlighted the area where Total Fertility Rates are shown and the footnote which confirms the numbers are Births per Woman.  Notice that here 3 decimal places are used with the TFR for All Australians as 1.789. For a table showing all countries of the world you might find just 1 decimal place used because of the wide variation in TFR around the world. In the case of the ABS publication, there is most likely interest in small changes of this relatively low TFR from year to year.

        The following 3 minute video gives a simple illustration of how Total Fertility Rate is calculated.
            
        You can now follow the same method used in the video, to calculate some Total Fertility Rates for Australia. Click on the Exercise sheet and follow the prompts.


        • 203.3 Alternative Fertility Measures

          Whilst the most universally used measure of fertility is the Total Fertility Rate, there are some other types of birth rates which you might come across. These are discussed below. They are generally only used where data available is not sufficient to allow calculation of age specific fertility which is used in the Total Fertility Rate calculation.

          Crude Birth Rate (CBR)
          Crude Birth is simply the number of registered births in a 12 month period, divided by total population (both males and females) in the middle of the period, expressed per 1000 of population.
          Crude Birth Rate is the most basic measure for comparing Fertility from one country to another  It was used for early years of World data on fertility before age and sex based population data became available for a wider range of countries, which enabled more specific measures.
          General Fertility Rate (GFR)
          General Fertility Rate is an improved version of CBR by using just Females of childbearing age in the denominator of the calculation. Traditionally, child bearing age used has been age 15 to 44 but with IVF producing increased births to women in their 40s, the range is being extended to age 49 in most statistical agencies.
          Whilst in most cases, both a male and female parent are involved in the conception of a baby, the physiological impact and social disruption on the female is considerably greater than for the male parent. It is also more reliable to collect birth data specific to the mother than the father. This is why the fertility rates generally preferred by demographers are rates referenced to women of reproductive age.
          Child Woman Ratio (CWR)
          Some countries do not have reliable registration systems for births but they might conduct a census every few years which gives population head count by age and sex. The Child Woman Ratio is a proxy measure for birth rates by comparing children under age 5 to the number of women of reproductive age. This rate might be expected to be about 5 times the true General Fertility Rate, although if infant mortality is very high it would be less than that.  
          Situations where a demographer might use the Child Woman Ratio are in doing field research in remote areas or tracking fertility trends in war zones or after humanitarian crises where birth registration systems have been disrupted or records lost.
          Net Reproduction Rate (NRR)

          Demographers have a more complex version of TFR called Net Reproduction Rate (NRR) which allows for premature death (before reproductive age) and sex ratio at birth. A NRR of 1.0 implies mothers giving birth will produce the exact number of female births required to reproduce the numbers in their mother's generation. 

          • 203.4 Fertility in Developing Countries

            In the less developed world, women have less access to birth control and this leads to potential excessive population growth. It also reduces women's potential for productive employment and personal autonomy.  However, people in such countries may deliberatly aim for larger families to provide labour for family run farms and small businesses. Whilst there have been great reductions in fertility rates in many countries since the 1970s, rates are still very high in North-West and Central Africa.  The maps in the picture linked below, show that in 2014 the countries Mali, Burkina Faso, Chad, Niger and Somalia had Total Fertility Rates above 6 births per woman.

            This 3 minute video from Aljazeera highlights some of these issues using Senegal as an example.

              

            The following 2 page factsheet from Population Reference Bureau summarises the issues facing women in Senegal with regard to access to contraception and family planning.  These are the main explanations for the high Fertility rates experienced in this country.

            The following is a 24 page research paper on historical cultural issues influencing Fertility in North West Africa, led by Anthropologist Dr Sarah Randall of the London School of Hygiene and Tropical Medicine.

            • 203.5 Fertility in Developed Economies

              In more highly developed countries like Australia, women have (since 1970s) had equal access to employment and education, high standard of living, universal health care and expanding career opportunities. Safe and legalised access to abortion in medically and psychologically advised circumstances has also been available.
              This has meant most women in Australia have a full range of birth control options.  Those women who have achieved rewarding and satisfying employment careers have tended to defer family formation. The Australian cultural pursuit of home ownership has also encouraged couples both to extend full employment and defer family formation. These circumstances in Australia are a contrast to the type of fertility issues in Senegal.
              The following link reveals a graph of Age Specific Fertility Rates for Australia at 1970 and 2014. It shows an increase in the average age of mothers giving birth of 4 years between these years (from age 26 in 1970 to 30 in 2014). The Total Fertility Rate reduced from 2.86 in 1970 to 1.79 in 2014 (a reduction of 37%).
              Some key observations from this graph are as follows:
              • A general observation of demographers studying fertility is that the later women commence starting a family, the less their total births are likely to be. Take another look at the graph and see how the excess of the blue columns (1970) in early years compared to the red columns (2014) is not counterbalanced by the excess of red columns over blue in later years.
              • There is a declining capacity of women to give birth as middle age approaches. You will learn more about this in the following video and articles.

              This deferment of family formation has brought pressure to bear on medical technology to solve reproductive issues of conception at later ages. In the following 10 minute video, two leading reproductive scientists highlight the rapid decline in fertility and healthy reproductive outcomes for both men and women as ages increase. The scientists are Dr Melanie McDowell and Laureate Professor John Aitken.
                 
              This next 7 minute video highlights contemporary social issues associated with fertility in Australia. It is a panel discussion with a social researcher (Mark McCrindle) and a medical fertility researcher (Professor William L. Ledger) at UNSW in Sydney in 2015.

               

              The following is a 4 page extract from the 2010 Magazine of The Royal Australian & New Zealand College of Obstetricians & Gynaecologists which summarises the issues related to working career women and optimum family planning in the developed world countries like Australia with high access to fertility control technology.



              • 203.6 Family Size, Childlessness and Population Growth

                In the previous Topics you were introduced to Fertility rates. What you may now be curious to ask is what impact Fertility rates have on population growth?
                A common perception is that if a husband and wife have on average 2 children, the population should eventually stop growing and be at a stable level (ignoring any impact of migration for now).
                It's not quite as simple as that for the following reasons:
                1. Premature Death: Not all female children may survive until reproductive age and some may die before completing their full future potential level of fertility.  This means those couples where the female lives through to their late 40s need to have more than 2 children to offset this.
                2. Childlessness: A second reason is that some females may choose to not have children at all or may be found biologically incapable of bearing children. A further explanation is that although they may be biologically capable of giving birth they may become absorbed in satisfying careers which overtake their desire to reproduce or they leave it too late to do so.
                Here is an approximate way to illustrate these factors:
                1. Premature Death Allowance: Based on Australian Life Tables 2010-12 the probability of a female dying before age 50 is 2.5%.  So the 'stable population' target for family size planning purposes needs to be 2.6% higher (1/[1-0.025]) to compensate for this.
                2. Childlessness Allowance: The link below provides the latest (2006) detailed analysis of Childlessness for Australia by the ABS. It shows that in early 1900s about 30% of women were childless and this has declined to about 11% in 1996. The introduction to the article quotes estimates by ABS that 24% of women entering reproductive years in 2000 might never have children. In other words, using the 24% prediction,  the women who do have children in future would need to have 32% (1/[1-0.24]) more children to make up for this. This means the notional 2 child 'stable population' target for family size planning purposes, to compensate for Childlessness & Premature Death needs to be  34.6% higher (2.6% + 32%) at 2.7 births for those women who do have children. 

                The latest historical family size data current for Australia (see link below) is the "number of children ever born" which is collected in every second Census. The latest figure is as at 2011 for female parent at the end of reproductive period (age group 45 to 49). This shows 2.3 children per parent and 14.8% of parents childless at that age group.  You might ask "Why is this figure of 14.8% much lower than the ABS expectation of future childlessness of 24% in the 2006 ABS article discussed above?".  The 24% figure is effectively a 35 year prediction while to obtain actual historical figures for Childlessness takes a long time because we need to have 35 years of past data to cover a woman's reproductive life. In the case of the 2011 Census figure, this covers years of giving birth from 1976 to 2011.  Social and economic issues associated with variation in Childlessness over time are discussed in the ABS article.

                Based on the 2011 Census level of Childlessness of 14.8% (rather than 24% projected for the future in 2006) and the 2.6% Premature Death factor, the notional two child stable population family size target would be is 2 x (1+2.6%+17.3%) which equals 2.4 children per family. So our conclusion for this past reproductive period covering all ages of women from 15 to 49 (calendar years 1976 to 2011) is that the family size average of 2.3 is very close to that estimated for achieving a stable population (ignoring migration and the extra living population due to extended life times from mortality improvement). These extra factors are studied in the 300 category of Population Dynamics courses.
                From the discussion in this topic you will see that world population growth and family planning targets are a bit more complex than just observing Total Fertility Rates.  Total Fertility Rates are still the best comparator of birth rates at country level and over time but we need to remember TFR effectively spreads births over all women whereas discussion of family planning and number of children are often discussed in the context of women who have (or intend to have) at least one child.

                • 203.7 What's Next?

                  In this Course 203 you started your journey in demographic rates with the beginning of human life - Birth Rates.  You covered a number of different ways of representing births and settled on Total Fertility Rate as the most universally accepted measure of Fertility. You also saw that there is a need to understand what particular words mean in the context of Demography. Don't forget you can always go to the Glossary to find out what words mean in the context of Demography.  There is a Glossary link in the Course Guide side box.
                  In the next Course 204, you will follow a similar path to Fertility as we move on to study Survival Rates (often described in Demography as Mortality). Just check that you have completed all the activities in this Course before moving on.
                  Click the following link to go to 204 Life Stage Mortality.