Population Pyramids
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Population pyramids graphically represent the age and sex composition of a population. They take different shapes depending on factors like growth rate, life expectancy, and mortality rates. As countries develop economically and medically, their population pyramids typically evolve through stages from broad bases with high birth and death rates to more rectangular or even inverted shapes with low rates. This demographic transition is driven by declining mortality leading to rapid growth, then later lower birth rates as well.
Population Pyramids
- 1. Population Pyramids = graphic device that represents a population’s age and sex composition. Pyramid describes diagram’s shape for many countries in 1800’s when was created.
- 2. A broad base of younger age groups and progressively narrowing to apex as older Populations were thinned by death. Now there are many different shapes.
- 4. Quickly growing population of Kenya – jas ,most people in lowest age cohorts Percentage in older age groups declines successively with markedly sloping sides. Typically female life expectancy is decreased in older cohorts of less developed countries – 50 for Kenya – proportion of females in older age groups is less than in Sweden or U.S.
- 7. In wealthy countries with very slow rate of population growth – population is nearly equally divided - so pyramids have Almost vertical sides. War can be reflected by showing depleted age cohorts and male – female disparities. The % of a country’s population in each age group strongly influences demand for goods and services within that national economy. Country with high % of young has high demand for educational facilities and health delivery services.
- 8. Dependency Ratio = measure of # of dependents – old and young that each 100 people in productive years (15 – 64) Must support. Population Pyramids show this. Population pyramids also foretell future problems from present population policies or practices. Ex. China’s population policies skewed in favor of males.
- 11. Natural Increase = Rate of Natural Increase of population – derived by subtracting The Crude Death Rate from the Crude Birth Rate. Natural means increases or decreases due to migration are not included. This rate is usually expressed as a % or rate per 100 rather than 1,000. Doubling Time = Time it takes for population to double.
- 12. Ex. – 2% rate of increase – recorded 1999 by developing world except China Population would double in 35 years – since 1% rate would take 70 years to double. Population Doubling Time – estimated by dividing the Growth Rate into the number 70 = ( 70 divided 2 = 35 years). Globally – Rates of Increase have risen over history. Thus – doubling time has decreased.
- 13. Should world fertility rates decrease - - as have recently – population doubling time Will correspondingly increase as it has since 1990. Even small annual additions accumulate to large total increments because of geometric or exponential (1,2, 4, 8) instead of arithmetic growth. Inevitable consequences of doubling or J-Curve Growth.
- 15. The Demographic Transition – some form of braking mechanism must operate to control totally unregulated population Growth – voluntary or involuntary. Demographic Transition – voluntary relation between population growth and economic development. – traces changing levels of human fertility and mortality associated with industrialization and urbanization.
- 16. This model assumes over time – high birth and death rates will slowly be replaced by low rates. The 1st Stage = of process – and demographic transition model – characterized by high birth and high but fluctuating death rates. When births only slightly exceed deaths – the population will grow only slowly. From 1 AD to 1650 – for population to increase from 250 million to 500 million = Doubling Time of over millenium and a half. Offset by sometimes catastrophic decline – like bubonic plague. This 1st Stage no longer found in any country.
- 17. This model was developed to explain population history of Western Europe. Western Europe entered 2nd Stage with industrialization 1750 – it’s effects – declining death rates with high birth rates have dispersed worldwide without universal industrial economies. Rapidly increasing population during 2nd Stage results from dramatic increases in life expectancy. This reflects falling death rates due to advances in medical and sanitation practices, rising per capita incomes, urbanization that provides environment where medicine and food distribution improvements are concentrated.
- 18. Birth rates don’t fall as soon as death rates – cultural patterns change more slowly than technologies. Many Latin American and South and Southwest Asian countries show charcteristics of 2nd Stage. Annual rates of increase of these countries are near or above 30 per l,000 and their population will double in 20 to 25 years. Means underdeveloped societies have been beneficiaries of life preservation techniques.
- 19. Third Stage = when birth rates decline as people begin to control family size. Urban, industrialized societies may view kids as economic liabilities, instead of assets as agrarian societies do. When birth rate falls and death rate remains low – population size begins to level off. 4th Stage – End of model – final stage – characterized by very low birth and death rates. This results in very slight % increases in population and doubling times stretching to l,000 years or more.
- 20. Extension of 4th Stage into 5th Stage – population decrease has so far been confined to rich, industrialized countries Throughout the world – Europe and Japan. By 2010 – most world’s population growth will result from Demographic Momentum – not 2nd Stage expansion. Original model made to describe Northwest European countries as went from rural-agrarian to urban –industrial.
- 21. Beginning 1860 – lst death rates then birth rates began gradual decline. = Mortality Revolution – first came as epidemiological transition echoed demographic transition to which it’s associated.Many formerly fatal epidemic diseases became Endemic = continual within a population. As people developed partial immunities –mortalities with them declined.
- 22. Health of European population increased with improving animal husbandry, crop rotation, etc… Sewage systems, sanitary water supplies – common in larger cities – hygiene improved everywhere. Deaths associated with chronic illnesses associated with maturing and aging population increased. Passed to Age of Degenerative and Human-Origin Diseases.
- 23. Increases recently in drug and antibiotic resistant diseases, pesticide resistance Of disease-carrying insects, and AIDS cast doubt on finality of “ultimate” stage. In Europe – decrease in death rates was echoed by decreases in birth rates as societies altered traditional concepts of ideal family size.