The Human Population: Patterns, Processes, and Problematics Lecture

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The Human PopulationPatterns, Processes, and
ProblematicsLecture 13 Part III Population
Structure Characteristics1) Age Sex2)
Population Aging the life course3) Family
Demography Life Chances4) The Urban Transition

• Paul Sutton
• psutton_at_du.edu
• Department of Geography
• University of Denver

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The Age Transition(another component of the
Demographic Transition)

• The Age Transtion represents a shift from a very
  young population in which there are more males
  than females to an older population with more
  females than males. In between there are bumps
  and dents in the age and sex structure that
  represent powerful forces of social, economic,
  and political change and a source of
  demographic change as well.
• The interaction of fertility, mortality, and
  migration produce the age and sex structure of a
  population a record of past history and a
  picture of potential future situations.

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Age Stratification Cohort Flow

• The idea that societies have separate sets of
  expected roles and obligations for people of
  different ages is captured by the concept of Age
  stratification, whereas cohort flow captures the
  notion that at each age we are influenced by the
  historical circumstances that similarly affect
  other people who are the same age.

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How real is Age Stratification?

• The age stratification theory begins with the
  proposition that age is a basis of social
  differentiation in a manner analogous with social
  class. The term stratification implies a set of
  inequalities , and in this case if refers to the
  fact that societies distribute resources
  unequally by age. These resources include not
  only economic goods but also such crucial
  intangibles as social approval, acceptance, and
  respect. This theory is not a mere description of
  status, however it introduces a dynamic element
  by recognizing that aging is a process of social
  mobility.
• As the individual ages, he(she) too moves within
  a social hierarchy. She goes from one set of
  age-related social roles to another and at each
  level receives greater or lesser rewards than
  before.
• In contrast to other forms of social mobility,
  aging is inevitable, universal and unidirectional.

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Demographic, Social, Economic Phenomena that
vary with age
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Some Age Stratification Questions

• Since income (power) increase with age how might
  a very young population like Mexicos differ from
  an older population like the U.S.?
• A few hundred years ago European society had
  essentially 3 age strata Infancy, Adulthood,
  Old Age Power was concentrated with the Old Age
  Strata
• Modern Western societies seem to have at least 7
  age strata Infancy, Childhood, Adolescence,
  Young Adulthood, Middle Age, Young-Old, and
  Old-Old Power is Concentrated in Middle Age
  Young-Old
• Are we evolving to a Culture of Youth with Power?

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Age Stratification can vary with Cohort Flow

• When my dad says to me Son, when I was your
  age. I interrupt him and say Dad, You were
  never my age.
• A Cohort refers to a group of people born during
  the same time period.
• Each cohort starts out with a given size which,
  save for additions from immigration, is the
  maximum size it can ever attain. Over the life
  course of the cohort, some portion of the its
  members survive, while others move away or die
  until the entire cohort is destroyed. Each cohort
  starts out also with a given composition it
  consists of members born with certain
  characteristics and dispositions. Over the life
  course of the individual, some of these
  charactersistics are relatively stable (a
  persons sex, color, genetic makeup, country of
  birth, or at entry into adulthood in our
  society the level of educational achievement
  are unlikely to change) When successive cohorts
  are compared, they resemble each other in certain
  respects, but differ markedly in other repsects
  in initial size and composition, in age-specific
  patterns of survival (or longevity), and in the
  period of history covered by their respective
  life span.

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The Lexis Diagram(I find this fairly useless)

• A graphical device for comparing Period vs.
  Cohort Information

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Age Cohort Age Strata Interaction

• As cohorts flow through time,
• Their respective sizes and
• Characteristics may alter the
• Allocation of status and thus
• The socialization into various
• Age-related roles because each
• cohort is moving through history
• together, whereas each separate
• cohort is moving through a different moment in
  history. The life experiences of cohorts born in
  1900, 1920, and 1940 vary dramatically. As they
  move through time , the characteristics of
  cohorts may change in response to changing social
  and economic conditions will influence the
  formation of new cohorts. This continual feedback
  between the dynamics of successive cohorts and
  the dynamics of other changes in society produces
  a constant shifting in the status and meaning
  attached to each age stratum, providing an
  evolutionary link between the age structure and
  the social structure.

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More Cohort Factoids

• Common names for Cohorts The Great Generation
  (The WWII adults), The Baby Boomers,
  Generation X, Millenials
• What does Age Structure Cohort Dynamics say
  about the Baby Boom generation what happened?
• Easterlins Relative Cohort Size Hypothesis
  Suggested that Larger cohort would increase
  supply of labor relative to demand and thus
  depress wages and leave boomers less well off
  than their parents.
• Did this happen? NOBoomers adjusted by 1)
  Delaying marriage, 2) Postponing children in
  marriage, 3) Sending women to work. Downsides1)
  Not Financially ready to retire Higher suicide
  rates

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Sex Gender

• It is a common assumption that there are the same
  numbers of males and females at each age
  actually this is rarely the case. Migration,
  Mortality, and Fertility operate differently to
  create inequalities in the ratio of males to
  females (the sex ratio)

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Fertility the Sex Ratio

• Sex Ratio is 104 110 in all human societies
• U.S. rates lower, Asian rates higher
• We dont know why.
• Data on miscarriages and fetal deaths suggest
  that more males conceived than females
• Males have higher death rates from conception
  onward. Higher sex ratio may be cause or result
  of this fact.
• Main Conclusion Men outnumber women in the early
  years of a cohort.

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Mortality and the Sex Ratio

• Men have higher death rates that women at every
  age throughout the life cycle.
• As a cohort ages the sex ratio inevitably drops.
• This is why Cathy the cartoon character cant
  find a mate.
• In Canada, sex ratio is high because migrants to
  Canada are predominantly men.
• In Mexico, sex ratio is low because emigrants
  from Mexico are predominantly men.
• In U.S., women start to outnumber men in the
  25-29 age bracket.

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Sex Ratio as a function of Age
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Characterizing Age Structure

• Typically this is done with a Population Pyramid
• A population is YOUNG if 35 or more of its
  population is under 15 years of age.
• A population is OLD if 12 or more of its
  population is over 65 years of age.
• A population is AGING if the proportion of
  people over 65 is increasing.
• Key figures of Merit Average Age, Dependency
  Ratio, and Age Specific Growth Rates

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Global Patterns of Young Old Populations
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More Population Pyramids
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Figures of Merit that briefly summarize previous
pyramids

• Average Age (actually the median age)
• Nigeria 17.4 Mexico 23.3
• Canada 36.9 United States 35.7
• Dependency Ratio (Old Young) / (Working Age)
• Sample Population of 100 people 45 under 15, 3
  over 65
• Dependency Ratio is 48/52 or .92 (very much like
  Nigeria)
• Sample Population of 100 people 19 under 15, 13
  over 65
• Dependency Ratio is 32/68 or .47 (very much like
  Canada)
• Note Dependency Ration does not capture relative
  s of old Young

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China India(changes in Age Specific Growth
Rates 1980 2000)
Which country is in better shape and why?
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Stable Stationary Populations

• A Stable population is one in which the age
  specific birth and death rates do not change.
  This Means that the proportional look of the
  population pyramid does not change. However, the
  population could be growing or shrinking.
• A Stationary population is one in which it is
  both stable AND at zero population growth (its
  total size is not changing)
• Model Stable Population is often used as an
  assumption when limited measurements available

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Population Projections Forecasts

• A population projection is the calculation of the
  number of persons we can expect to be alive at a
  future date given the number now alive and given
  reasonable assumptions about age-specific
  mortality and fertility rates. (based on
  assumptions)
• Demographic theory is not now, nor is it likely
  ever to be, sophisticated enough to be able to
  predict future shifts in demographic processes,
  especially fertility and migration, over which we
  as individuals exercise considerable control.
• A population forecast is a statement about what
  you expect the future population to be.
• Forecasts of weather and earthquakes, where the
  next few hours are ths ubject of interest, and of
  unemployment, where the next year or two is what
  counts, are difficult enough. Population
  forecasts, where one peers a generation or two
  ahead, are even more difficult.

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Population Projection Methods

• 1) Extrapolation
• 2) Components of Growth
• 3) Cohort Component Method
• 4) Backward or Inverse Projection

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Extrapolation

• Plot known populations as a function of time
• Fit a mathematical function to the points.
• E.G. Pop(t) some mathematical function of t
• Function typically linear or exponential
• Plug in future t to calculate Pop.
• Note Does not work very well

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Components of Growth

• This is using the very fundamental population
  equation
• Problem How do you know future Birth, Death, and
  Migration Figures?

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Cohort Component Method

• This is the most sophisticated method of
  projecting population. You need a lot of
  information to do this including
• Complete Age Sex Structure of Population at
  some time (a population pyramid)
• 2) Age Sex specific Mortality, and Migration
  rates. And Age Specific Fertility Rates.
• 3) Can be tweaked by guessing how specific
  Mortality, Fertility, Migration rates will vary
  as a function of time.

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Cohort Component continued..
1995 2000
2005

• 2015
  2050

Cohort Component for Mexico with constant
fertiltiy (3.3) and constant Life Expectancy
(72.2) and constant annual out-migration (300,000)
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Backward or Inverse Projection

• Inverse projections can be done via any method
  (extrapolation, components of growth, or cohort
  component)
• Best methods use reverse cohort component in
  which a good Age Sex structure is obtained with
  best estimates of Age Sex specific Mortality
  and Migration rates and Age specific Fertility
  rates.
• Wrigley and Schofield used backwards estimates
  from 1871 census of England and Wales to prepare
  a demographic history of England.
• Whitmore used Inverse projection to determine
  that 90 of the population of the Basin of Mexico
  died in the first 100 years of European Contact.

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The Impact of Declining Mortality
Strangely enough Longer life expectancy Makes
the pyramid Wider at the bottom Assuming all
Other Things stay equal
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Declining Mortality continued
Declining Mortality Alone increases Absolute
numbers Across the board But much
more Dramatically at Very Young and Very Old.This
is Because changes In death rates not Equal
across the Board. Mostly due To lowered infant
Mortality rates
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Declining Mortality for U.S.

• Increased life expectancy in the U.S. (e.g. going
  from 65 to 75 is not really due to lower infant
  mortality but simply the fact that people live
  longer. This kind of change in mortality does not
  have the same kind of impact on the age and sex
  structure of the population.

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Declining Fertility Age Sex Structure

• Changes in
• Fertility has biggest
• long term impact on
• age and sex structure
• of a population
• whereas
• Migration has the
• biggest short
• term impact. This is
• changing fertility
• only with Life Expectancy of 40 years. This
  population would collapse disappear because 2.1
  Fertility not above replacement level

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Declining Fertility w/ Longer Life Expectancy (80
years)
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Saudi Arabia The stories in Pop Pyramids
through time

• Pop of 3 million just after WWII. Today 20
  million, TFR 6.1, Life expectancy 70 years.
  Massive in-migration of labor now. Massive
  out-migration of labor in the near future?

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Migration the Age Sex structure
What impact will this have on total U.S.
Population Pyramid?
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U.S. Population Pyramid with without migration
50 years from now
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City Scale Geography of Population Pyramids (San
Diego

• Match each neighborhood to the following
• Right near SDSU
• Suburban San Diego
• Just over border from Mexico with high immigrant
  population
• Downtown San Diego (similar to downtown Denver)

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Demography and Society

• It is through the mechanism of the age and sex
  structure that all demographic changes are
  translated into a forces with which me must cope.
  A high birth rate does not simply mean more
  people It means that a few years from now there
  will be more kids entering school than before
  that 18 years from now there will be more new job
  hopefuls and college freshmen than before. An
  influx of young adult immigrants this year means
  a larger than average number of older people 30
  or 40 years from now (and it may mean an
  immediate sudden rise in the number of births
  with all the attendant consequences).

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Population Momentum

• Young age structure populations have a momentum
  for population growth built into them. The 50 or
  so people under 15 years of age will probably
  survive and have children. Even if they reduce
  fertility to a replacement level of 2.1 the
  population will grow for a while. One way to
  measure momentum If a population were to
  immediately reduce its fertility to replacement
  how big would it grow to before it became
  stationary?
• Africa and Asia 1.56 times bigger
• United States 1.10 times bigger
• Population Momentum is the dominant force driving
  population growth in the world today. Only in
  Sub-Saharan Africa is the impact of high
  fertility greater than momentum

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Reading an Age StructureAfineresolution
PopulationPyramid for the United States
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Questions for Previous Slide

• Can you see the baby boom? Did it start with a
  bang?
• Why is it hard to see the Depressions impact on
  fertility?
• According to FBI data there were 50 more arrests
  in 1980 than in 1970? Had society fallen apart or
  does the Age structure explain this?
• When was the Baby Bust? (aka Birth Dearth)
• What social processes contributed to the Baby
  Bust?
• What was a good decade to be born in
  demographically and why?
• What is a hot political issue associated with the
  aging of the baby boom?

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Because I PromisedRacial Breakdown of U.S.
Population
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The Demographic Transitionas seen in Population
Pyramids
-?
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Next Up..

• Chapter 9
• Population Aging and the Life Course