Topic outline

  • 202 POPULATION COMPOSITION

    To go back to the previous Course, click the title here 201 Introduction to Demography.
    • 202.1 Composition Measures - Sex Ratio

      This course 202 covers descriptive measures of populations which may affect the type of detailed further analysis a demographer might choose to do. These measures are also used to explain differences between populations and changes in the one population over time.
      A first basic Ratio to look at is population Sex Ratio which is defined as the Ratio of Males to Females (usually multiplied by 100 and shown with 1 decimal place). A population with say 10,250,000 Males and 10,000,000 Females would have a Sex Ratio of 102.5 males per 100 females.
      The Graph below shows the Sex Ratio for Australia from early settlement days in 1800 when male convicts dominated the population. This was followed by some attempt to attract more women settlers to balance it. Then came the 1820-30s gold rush which attracted mainly men immigrants. Then followed a long period of rapid population growth through family settlers with high birth rates. This results in Sex Ratio trending down towards 100.

      As well as using Sex Ratio for the total population, it is also calculated for a cohort of new born babies and called Sex Ratio at Birth. Although there is no biological explanation for it, there are usually slightly more Males born than Females. This results in most countries having a Sex Ratio at Birth around 105. But over the lifetime, this balances out as Males generally experience higher mortality throughout life than Females. 
      A country with unusual Sex Ratio at Birth data is China. This is related to a strict one child policy implemented from 1979 to 2015. The official demographic statistics show very high Sex Ratio of reported births up to around 120 through this period. Some commentators have suggested this may have reflected male baby preference (there were some exemption for people in rural areas to have a second child if the first was a girl) and neglect or infanticide of female babies. More recent research indicates this unusual data may also reflect rural populations having more than one child and not reporting girl babies at time of birth. The link below is to the 21 page Research paper by John James Kennedy and Yaojiang Shi regarding this phenomena (if the whole paper is a bit much for you just read the Conclusion section from page 16). This illustrates why Demographers must understand how data is collected and shows how field research builds deeper understanding of demographics.
      • 202.2 Dependency Ratios

        Age distributions are one of the most commonly used demographic statistics. There are also a range of approaches to how they are presented in either tabular or graphic form. It is best to first of all have a full data-set by all individual ages and separation into male and female. This will give maximum flexibility as how age demographics are presented which will depend on the context.
        A first approach will be to present Dependency Ratios. This is usually done for males and females combined (i.e. persons).
        Three age group population totals are required to calculate Dependency Ratios as follows:
        1. Young (ages 0 to 14)
        2. Working Age (15 to 64)
        3. Aged (65 and over)

        There are then 3 different Dependency Ratios which can be calculated
        1. Young Dependency Ratio = Young / Working Age x 100
        2. Aged Dependency Ratio = Aged / Working Age x 100
        3. Total Dependency Ratio = (Young + Aged) / Working Age x 100
        We can then use these ratios to compare two populations at one point in time or track a single Ratio for one population over past and future projected time (and combinations of these two approaches).
        Dependency Ratios are a significant focus of governments when forming budgets and projecting the capacity of revenue raised from the working population to support education, universal health care, welfare and pensions for the Young and Aged populations.
        Sometimes when discussing adequacy to pay pensions, the Aged Dependency position might be expressed as X workers for every Aged person - this is effectively the inverse of the Aged Dependency Ratio.

        Click to access the following document which provides Exercises in calculating Sex Ratios and Dependency Ratios for Australia
        If you are not familiar with spreadsheets (which are required by the Exercises) you might find the following links to YouTube videos useful for help with using Microsoft Excel or Google Sheets.
            



        • 202.3 Age Distribution using Population Pyramids

          A more traditional detailed form of depicting age distribution is to assemble data by sex and 5 yearly age groups and draw a Population Pyramid.
          You will see how this concept is applied in the following 3 minute video.
           
          As described towards the end of the above video, indents and bulges in the shape of different countries pyramids can be explained by past aberrations in birth rates and death rates. Similarly changes in these rates over long periods for a country can change the whole shape of the country's pyramid. Some general principles are as follows:-
          • Constant high birth rates and high death rates result in a triangle with a wide base and a peak not as high as lower death rate countries. Examples are Nigeria or Rwanda.
          • A country with low death rates and medium birth rates changing to very low birth rates will have a narrow base expanding to wider middle and rounded top to include high number of people at older ages. An example is Japan.
          • A country experiencing very high recent migration will have an exaggerated wide middle as migrants are typically in the lower half of the working age population. An example is Australia.

          Here is an easy way for you to draw Population Pyramids.  The US Census International site does all the hard work for you.  Open the Exercises Instruction sheet below (printing it out might make your work easier) and see if you can complete the 4 Exercises.
          • 202.4 Spatial Distributions

            Demography also involves study of geographic location of population - referred to as Spatial Demography.
            Spatial population data is used extensively in urban planning and in providing government and health services for people in remote areas. In Australia you will find data on population in each Local Government area accessible from most Local Council web sites.
            In countries which have well developed representative democracies, spatial demographic data is legislated to be the determination of electorates and local government areas and the numbers of representatives per electorate, division or State. This is one major purpose of the legislated 5 yearly Census in Australia. 
            The Census data for each person is added into totals for a Statistical Local Area (SLA). An SLA is the smallest geographic region for which population data can be geographically located. The required Electoral regions can then comprise a large aggregation of SLAs to make the required size to satisfy electoral laws.  Population headcounts by State also determine allocations of federal government tax revenues (including GST).
            The two page document below describes the process used by the Australian Bureau of Statistics to measure population head count. The data accessed by demographers from the ABS Census has personal identification details removed and is aggregated in a way which prevents personal information being imputed from small area population data.

            The Australian Bureau of Statistics has a special section on Spatial Geography found here:

            The Australian population is more concentrated in major capital cities than many other comparable developed countries. At 2016 Census 66.6% of the population lived in the 8 State/Territory capital cities. A comparable World average is that 54.5% of world population lives in urban areas but the trend worldwide is for greater concentration of population in cities. The Australian trend is partly due to the lack of a modern diversified high speed rail network, preference for coastal living lifestyle and high immigration with new settlers preferring to live in major cities. Employment opportunities shifting from rural and manufacturing to service based industries are also relevant.
            • 202.5 Cultural Distributions

              The "Cultural" characteristics of population which are of specific interest to Demographers are indigenous (first nationals), religion, marriage and partnership and family structure. There is overlap in the study of these aspects with Anthropologists, Sociologists and Developmental Psychologists. 
              Demographers' interest is in quantifiable data, relating to variation in fertility and mortality rates which are associated with these Cultural characteristics. With regard to fertility, religion and family traditions can have significant influence on contraceptive practices, family size preference, baby sex preference and earliest age of conception.  With regard to mortality the demographic effect may be due to living more remotely in an unhealthy lifestyle and/or being far from the high quality health services available in major cities.
              Migration push and pull factors may also be influenced by culture. This may be because of being in a discriminated religious grouping or ethnic minority in an originating country or being attracted to a multicultural tolerant destination country.
              In Australia, the major demographic interest in cultural aspects is for people identifying as Aboriginal and Torres Strait Islander first nationals heritage. This has given rise to "closing the gap" policies by federal government to focus on reducing adverse mortality and health status. The biggest differences arise in relation to remote lifestyles and services. You can access the 2018 Report from the link below. It is rather long at 132 pages. Look at the first few pages of Chapter 6 starting from page 102. This Chapter covers some of the most significant issues in demography.

              The following item provides some exercises you can do in Spatial and Cultural distributions for Australian Population as at 2016.

              • 202.6 What's Next?

                You have now seen how demographers might analyse composition of a population before doing specific research on rates of birth and survival. The demographics you have covered in this course 202, answer questions like:

                • Is this an old or young population?
                • Have there been past traumatic Events likely to have distorted the age structure?
                • Does the population include different Cultures?
                • Are there likely to be geographic variation in demographic features?

                In the next Course 203 you will be introduced to detailed measurement of Fertility Rates.
                Click on the heading here to go to 203 Human Reproduction.