DEMOGRAPHY
I. Definition
A. Demography is the study of the
size, structure, and change of human populations
1. Size refers to
the number of people in the population
2. Structure can
refer to any of a number of ways of subdividing the population
a. For
demographers the most important kinds of structure are:
1. The
age structure: how many people there are of each age
2. The
sex structure: how many men there are and how many women
3. The
age-sex structure (a combination of the age and sex structures): how
many 0 year old males, how many 0 year old females, how many 1 year old males,
how many 1 year old females, and so on
b. For
practical purposes geographic structure is also important, e.g., how
many people live in
3. Change refers
to a change in the size or structure of the population
4. Human population
refers to some collection of people
a. Usually
all the people living in some specific geographic area
b. On
occasion used to refer to people defined other than geographically, for
instance, all sociologists; for our purposes we will restrict attention to
geographically defined populations
II. Demographic explanations
A. Though demography is a recognized subfield within sociology, its importance extends throughout sociology because of the wide usefulness of demographic explanations
B. A demographic explanation is an explanation of some social phenomenon in terms of the size, structure, and/or change of one or more human populations
EXAMPLES OF DEMOGRAPHIC EXPLANATIONS
1. James Q. Wilson in
the late 60s told politicians that they could promise that if elected they
would reduce the crime rate. The good news was that they could deliver on this
promise and that they wouldn't have to spend any new money to do so. The bad
news was that the crime rate would not start to go down until about 1980. As
2. My father's explanation of why Japan engaged in the expansionism in the 1930s that led to its involvement in World War II was that Japan's growing population and limited land base led to concern about Japan's ability to feed itself, which led to attempts to annex (by force) nearby agricultural lands. [The history book I consulted does not mention this theory.]
3. Why have
fundamentalist Protestant denominations been gaining so much ground in the
religious economy in recent decades? Is it because the mainline denominations
are doing something wrong (like secularizing)? Well, at least 75 percent of the
relative growth of the fundamentalist denominations is due to the fact that
their members tend to have more babies than mainliners (and most people adopt
the religion of their parents).
a. 75%
doesn’t explain the whole story, but it explains a lot
4. In a somewhat complex
theory, Guttentag and Secord (see Chapter 12 in Stark) argue that the nature of
cultural sex roles in a society is based on the sex structure.
C. Often one has to consider demographic explanations to guard against spuriousness in interpreting the effects other sociological factors
1. For instance, criminologists interested in drawing conclusions about the effects of longer prison sentences on crime rates have to make sure that any changes they see are not simply due to changes in the age structure
a. The criminologist may not be interested in the age structure, but she still has to think about it to make sure it is not responsible for the changes she is really interested in
D. Principles that give demographic explanations of behavior their power
1. People with
different demographic characteristics often tend to behave differently
a. "Demographic characteristic" will be defined later; for now think of it as referring to things like age or sex
b. Q: which of our examples above is built on this principle?
A:
A’:
This also applies to explaining why there are so many religious fundamentalists
2. Societies and
individuals continuously adapt to the size and structure of the population
a. (Corollary)
Changes in population size or structure are likely to result in changes in
social behavior and other elements of social structure
b. Q: which of our examples above is built on this principle?
A:
A’:
This would also apply to explaining the growing political power of religious
fundamentalists
c. Imagine the difference between the courting behavior of young women at Surf City, where there are two girls for every boy--which means girls can't be so choosy--, and Beefsteak Island, where there are two boys for every girl
III. Focus of Demography
A. The main question of demography: How do populations grow?
B. Subsidiary question: What are the consequences of population structure?
C. Populations change size in only three ways:
1. Births -- add to population
2. Deaths -- subtract from population
3. Migrations -- add or subtract, depending on if the move is in or out
D. Population change is summarized in the Demographers' Estimating Equation:
Population at some
time =
population
at some earlier time
+
births between the two times
-
deaths between the two times
+
in-migrants between the two times
-
out-migrants between the two times
YA GOTTA KNOW THIS!!
1. Called the "estimating equation" because it is used to make population projections (that is, estimates of the population)
2. We can use it for estimation because we know the number of births from birth certficates and the number of deaths from death certificates, we can guess net migration in several ways, and we regularly count the entire population
a. Net migration is in-migrants minus out-migrants
b. In
the US we count the population in years ending in 0
(1)
Done in the Census of Population, conducted every 10 years since 1790
(a)
Since it’s done every 10 years, it is also called the Decennial Census
IV. Demographic events
A. Demographic events are things
that happen to individuals that directly or indirectly affect the size or
structure of the population
1. The more direct the
connection, the more important the event is to demographers
B. The three most important demographic
events are birth, death, and migration
1. Important because they
are the only way a population can change size
2. Importance is reflected
in the DEMOGRAPHERS' ESTIMATING EQUATION
3. Importance is also
reflected in the three main branches of demography:
a. Mortality
-- the study of the death experiences of populations
b. Fertility
-- the study of the birth experiences of populations
c. Migration
studies -- the study of the migration experiences of populations
C. Other demographic events include:
1. getting older
a. Powerful
principle: every year everyone living grows one year older
1. Simple-minded
idea with profound consequences
a. WHY?
Because behavior changes with age
2. getting married,
getting divorced, getting separated
3. graduating, getting a
job, losing a job
4. getting sick
5. The important ones to
remember are getting older and getting married
V. Demographic characteristics
A. Demographic characteristics are
attributes of individuals that directly or indirectly affect the rate of
occurrence of demographic events
1. Most important are
attributes that most directly affect birth, death, and migration, since these
are the most important demographic events
B. MOST IMPORTANT: AGE and SEX
1. Age
a. Relations
to main three events:
1. Old
people are more likely to die
2. People
in the early adult years are most likely to have children
3. People
in the early adult years are the most likely to move
b. These
age differences are not dinky -- they're HUGE
c. Relation
to other demographic events: young adults are most likely to marry, older
people are the most likely to get sick
2. Sex
a. Relations
to three main events:
1. Only
women give birth
a. It
sometimes seems demographers only care about women because only women have
babies
2. Women
tend to live longer
a. Historically
this has not always been true because of high rates of childbearing and the
large risks associated with childbirth
3. Male
migration is on average for greater distances and is more likely to cross
international borders
b. Relations
to other events: divorced women are less likely to remarry than divorced men,
women are less likely to get a job
c. Other demographic characteristics
1. Marital status -
affects births
2. Race - in the US
African Americans live less long; African American women have about half a baby
more than white women; African American migration patterns differ from the
patterns for whites
3. Educational level - numerous
effects; especially important is that higher levels of education are associated
with lower levels of births
4. Health - sick people
are more likely to die
5. Especially important in
the
6. Note that many of these
demographic characteristics are triggered by demographic events (e.g., a
marriage changes your marital status)
Working with Demographic Data: Rates and Ratios
I. Motivate reasons for working with rates instead of straight numbers
Q1: When was the
A: 1976
Q2: Did more people die in the
A: In 1976, when 1.9 million died. The whole 1776 population was only 3.9 million
Q3: Looking at the number of deaths didn't seem to help us tell the good times from the bad. Why not?
A: Because the difference in the total population (218 million vs 4 million, more than 50 times as big) outweighs differences in chances of dying.
We want to be able to make useful comparisons between
countries with different sizes. For instance, we'd like to see whether an
individual's chance of dying was greater in 1776 than in 1976. We do this with
rates. Demographers are almost always more interested in rates of
demographic events than in the actual counts of such events.
Obstetricians
and morticians may care about the actual number of babies or bodies, but
demographers usually don’t
II. Rates
A. The general form of a demographic rate is:
RATE = (# of events in a period
of time / population at risk) * K
III. Ratios
A. Demographic ratios are often used when
analyzing demographic characteristics
B. The general form of demographic ratios:
RATIO = (# of people with some
characteristic / # of people with some other characteristic) * K
C. Interpretation: number with the
characteristic per K with the other characteristic
IMPORTANT EXAMPLE: THE SEX RATIO
SEX RATIO = (# males /
# females) * 100
Q: What would a sex
ratio of 95 mean? (This was the 1990 sex ratio in the US)
What would a sex ratio of
105 mean? (This was the sex ratio in the
IMPORTANT SEX RATIOS
Sex ratio at
birth = 105 (in the
US sex ratio,
2001 = 100 * (139,813,000/144,984,000) = 96.4
IV. Special Topic: proportions vs percents
A. PROPORTION
1. Numerator plus complement forms denominator [the
complement of A is "not A"]
P = (A / (A+~A))
or P = A / TOT
2. The formula P * TOT = A is extremely
convenient
B. PERCENT
1. PERCENT = proportion
* 100
2. People these days
tend to be able to think in percents rather than proportions
3. Calculator hint: divide
the denominator by 100 before entering into the calculation
Mortality
I. Mortality is the death experience of a population
A. The term is also used to refer to the
branch of demography that focuses on deaths
B. MOST IMPORTANT FACT ABOUT MORTALITY: Age
is strongly related to the chances of dying; excluding the first year of life,
the older you are, the greater your chances of dying.
C. Measures of mortality
1. Counts of deaths during
a period
a. 2,419,000
in US in 2001
2. Crude death rate
a. Remember
why this is CRUDE -- it does not take into account the age-sex structure of the
population
b. Age-specific
rates allow us to account for age
c. In
2001: 8.7
Remarkably stable: <9.0 since 1975, once (1992) as low as 8.5
2. Age-specific rates
Q1: Are your chances of
dying greater if you are living in Mexico or if you are living in the US? How
do we go about answering that question?
A: We
answer the question by examining crude death rates. The CDR in the
Q2: Does this mean that
Mexico is a healthier place to live? If not, why is the CDR lower in Mexico?
A: Mexico
is probably NOT a healthier place to live, because at every age your chances of
dying are higher in Mexico. For example, an average 20 year old in Mexico is
more likely to die than is an average 20 year old in the US. The CDR is lower
in Mexico because the average age in Mexico is so much lower than in the US.
Thus the US has more old folks, the people most likely to die.
a. We
made this comparison in terms of age-specific death rates, that is, death
rates for people of a specific age
ASDR(x)date = (# deaths during
date to x year olds / # x year olds in the population) * 1000
Interpretation: ASDR(15-24)1996 = .846;
ASDR(45-54)=4.284 In 1996 in the US, 0.8 of every thousand people aged 15 to 24
died. In that same year, 4 of every thousand people aged 45 to 54 died.
b. Since
the age-specific death is the probability of dying at a certain age, we can
graph the hugely important relation between age and the probability of dying
using age-specific death rates
LOOK AT OVERHEAD
1. Things
to note:
! The
probability of dying is relatively high in the first year of life. This
probability is not matched again until well into adulthood
! The
probability of dying throughout the rest of childhood is very low and really
doesn't change much throughout childhood
! Once the
probability of dying begins to increase noticeably, it really takes off
- More
precisely, not only does your probability of dying increase from one year to
the next, but also the amount by which this year's mortality exceeds last
year's gets bigger from one year to the next (second derivative is positive,
for those who remember their calculus)
! The rates
on the graph are from the US. The actual line would vary from country to
country, but the shape is universal: high first year mortality, low childhood
mortality, mortality first gradually then rapidly increasing through the adult
years
c. The
infant mortality rate is slightly different from the age-specific death rate
for zero year olds
INFANT
MORTALITY = (# deaths to zero year olds / # of live births) * 1000
1. The
US infant mortality rate of 6.8 in 2001 means that for every 1000 babies born
alive in 2001 there were about 7 children not yet one year old who died in 2001
(though possibly born in 2000). The
3. Other-specific rates
a. Age-specific
rates are only one way of usefully narrowing the definition of the population
at risk
b. Sex-specific
death rates look at mortality within one sex
c. Race-specific
death rates look at mortality within races
d. Age-sex-specific
rates look at mortality for one sex at one age
IMPORTANT PRINCIPLE: demographers
care about age- and sex-specific rates because the rates of occurrence of the
important demographic events are different for different ages and sexes
4. Life expectancy
a. The
usual statistic that demographers use to summarize the long term mortality
experience of a population is life expectancy
1. We
use it especially if we interested in comparing two groups to see which lives
longer
b. Life
expectancy is based on age-specific death rates. Basically you start with
100,000 people and figure out how many you would lose in the first year (on the
basis of age-specific death rates), how many in the second year, how many in the
third year, and so on until they're all dead. Then you add up all the years of
life these 100,000 people "lived" and divide by 100,000 to get the
mean number of years they lived
1. This
is LIFE EXPECTANCY AT BIRTH
a.
2001: 77.2 (79.8 female, 74.4 male)
2. The
same calculations can be used to tell how many more years you can expect to
live (on average) if you are now 20 or 40 or any other age.
a. 2000:
age 20=55.2 yrs for males, 60.3 females; age50=27.9 males, 31.8 females
SOURCE:
Statistical Abstract of the
5. Cause-specific death
rates
a. There
is great practical interest in what people die of
b. We
examine causes of death in terms of cause-specific rates
CAUSE-SPECIFIC
RATE = (# deaths due to cause / total population) * 100,000
c. The
cause-specific rate for a cause tells the chances a person will die of that
particular cause
d. Three
general categories of cause of death:
1. Infectious
disease
2. Contagious
disease
3. Other
(accidents, suicide, homocide)
e. In
the developing world, most people die of contagious diseases; in the developed
world, most die of degenerative
II. Important general facts about mortality
A. The probability of dying is
strongly related to age
1. This is one of the
strongest relationships in all social science
B. The first year of life is particularly
perilous
1. In the
C. Women tend to live longer than men
1. There are a few
societies where women and men have roughly equivalent life expectancies. These
are societies with high birth rates and high rates of death during childbirth
and where women are not highly valued
D. People in the industrialized world
tend to live longer than people in the third world
III. Important additional facts about mortality in the
A. Heart disease, cancer, and stroke
account for about three fifths of deaths
1. Heart disease 30%,
cancer 23%, stroke 7% (2000)
2. These are the leading
killers in most of the industrialized world
3. Infectious diseases
like malaria, dysentery, TB lead the way in the third world
a.
B. Infant mortality is embarrassingly
high
1. 14th among nations with
10million or more population
SHOW OVERHEAD
C. White life expectancy is higher than
African American
1. BUT, CDR is lower
for African Americans than for whites... WHY? (they are younger)
2. Age-specific death rate
is higher for African Americans at all ages, expecially infants, until about
75, when they are less likely to die than same aged whites
IV. Reasons for declining world mortality
A. From before the time of Chirst until a
couple of hundred years ago, mortality rates were pretty much steady (and
extraordinarily high by today's standards)
1. Stayed high in the less
developed world until around 1900
B. Three factors are principally responsible
for reducing mortality:
1. Improved public
health practices
a. Especially
clean water and sanitary disposal of wastes (good sewers)
2. Improved nutrition
a. Good
nutrition makes it easier to fight disease
b. Population
explosion of Industrial Revolution due to improvements in agriculture (to a
large extent), which led to improved nutrition
3. Improvements in
medicine
a.
Discovery of antisepsis especially important
Not nearly as important in public health practices and nutrition
FERTILITY/NATALITY
I. Fertility
A. Fertility is the actual birth performance
of a population
1. Also refers to the
branch of demography that studies births
B. Natality is a term also used
1. With a root that means
"to be born," natality implies an emphasis on the newborn. Fertility
implies an emphasis on giving birth
2. Giving birth is
sociologically more interesting than being born because moms (and dads) engage
in a lot more decision making regarding the birth than do babies
II. Fertility measures
A. The simple count of births we get
in the
1. In US in 2002,
4,021,726
a. Down from
4,025,933 (2001) and 4,058,814 (2000)
b. Most recent peak: 1990 -
4,158,212
c. Post-1960 peak: 1961 -
4,268,326
B.
Crude birth rate (CBR)
1. (# births / Population) * 1000
2.
World range in latest 2001 US Census Bureau estimates (for countries of
10 million+):
a. 50.7 in
3. US in 2002 was 13.9, lowest ever
recorded (less than 15.0 since 1995)
[(4,021,726 / 288,368,706) *
1000]
a. Recall that CDR was 8.7
b. Thus there were (13.9 - 8.7)=5.2 more births
per 1000 population than deaths. This is the Crude Net Natural Increase Rate
(or Crude Rate of Net Natural Increase)
c. Changing per 1000 to per 100 (percent) we
see that, excluding migration, the
Q: justify that conclusion
4.
Most of subsaharan
C.
General Fertility Rate (GFR)
1.
CBR tells how fast a whole population is having babies
2.
We need something else to find out how likely potential moms are to
actually have a baby : the General Fertility Rate (GFR)
GFR = (#births / #women aged 15-44) *
1000
3.
Around 70 in the
4.
Over 200 in some parts of the world -- 1 woman in five of child bearing
age has a child in any year!!
D. Age-specific Fertility Rate (ASFR)
1.
Since fertility varies so much as a woman moves through her fertile
years, it is useful to use age-specific rates when examining fertility
ASFR (x) = (# babies born to
x-year old women / # of x-year old women) * 1000
a. REMEMBER: we care about age- and
sex-specific rates because so much of the behavior we are interested in varies
greatly by age and sex.
2. Plotting the age-specific rates against
reveals a pretty universal graph
SHOW OVERHEAD (AGE-SPECIFIC
FERTILITY)
a. This overhead shows two lines, one for
b. Things to notice:
• The shape, an upside down V, is the same for
both countries
- This is virtually universal
• Fertility peaks around 25
• The most important difference between low
fertility
E.
Total Fertility Rate (TFR)
1.
Just as age-specific death rates are combined to create a useful summary
measure of mortality (LIFE EXPECTANCY), so can age-specific fertility rates be
combined to create a useful summary measure of fertility, the TOTAL FERTILITY
RATE
2.
TFR = ASFR for 15 years olds + ASFR for 16 year olds + ASFR for 17 year
olds + ... + ASFR for 44 years olds
a. That is, the sum of the number of babies
1000 women would have at each year during their reproductive life time
3.
The Total Fertility Rate is an estimate of the number of babies that
1000 women would have during their lifetimes assuming that age-specific
fertility rates do not change and that they live all the way through their
reproductive years
a. TFR for the whole world is about 2690.
Q: how many babies will the average world woman
have in her lifetime? How did you calculate it?
A: 2.69 babies per woman; since the TFR
describes 1000 women, divide by 1000 to get the number for 1 woman
This number has
dropped remarkably since I’ve been teaching: started at around 3500
4.
Often TFR is given as babies per woman instead of babies per 1000 women
a. This is how you see it in the newspaper.
Newspaper discussions of fertility almost always use the total fertility rate
b. World high: 8.0 in
c. World low: 1.10 in
SOURCE: http://www.un.org/esa/population/publications/wpp2002/wpp2002annextables.PDF
5.
TFR in the
a. For a population size to stabilize, there
must be exactly 1 daughter per woman for a long time
1. This idea ignores population change due to
immigration
2. Since there are more boys born than girls
and since women do not always live all the way through their child bearing
years, and since daughters may die before they reach childbearing age, a TFR of
2110 is needed for births to keep up with deaths over the long run
a. This hasn't happened in the
b. Much of the industrialized world is facing
the same problem
III. Why have children?
A.
One factor affecting a society's fertility is the value children have
for people in the society
1.
In traditional societies children are economic assets, providing needed
hands for farming or hunting
SHOW OVERHEAD 55: Why the
Poor Need Children
Overhead shows the average
age in Indonesia at which children begin to engage in various activities that
are beneficial to the household
NOTE that kids begin to make
agricultural contributions starting at 9 and hard cash contributions starting
just before 13
2.
In industrialized nations children are economic liabilities
a. When you have a baby today, people don't
say, "Lucky you, pretty soon you'll be able to put in another 10
acres." No, they say, "Have you set up a fund for your kid's college
education? You can never start socking away the dough too soon!"
b. Children today in the
1. Often called luxury items because
they're so expensive and give so little economic value in return
IV. Important facts about fertility
A.
Only women have children
B.
Only women of child bearing age (15-49) have children
C.
Married women have higher fertility than unmarried
1.
IMPORTANT EXCEPTION: today there is little difference between the
fertility of married and unmarried African American women
D.
The more economically valuable children are, the higher the fertility
E.
The more educated a person or population, the lower the fertility
SHOW OVERHEAD #41, FERTILITY
AMONG MARRIED AMERICAN WOMEN
NOTE: education doesn't always
reduce fertility; fertility can reduce education, as women drop out of the
educational system to bear and raise children
F.
There are more boys born than girls; the sex ratio at birth is about 105
1.
Sex ratio is closer to 100 in
G.
Total world fertility is about 2.7 babies per woman
H.
Total fertility of about 2.1 babies per woman is required for stable (no
growth) population
MIGRATION
I. One move is two events: in-migration and out-migration
A.
in-migration = immigration
B. out-migration = emigration
C. Place you left is the donor location
or origin
D. Place you are going to is the destination
II. Three general approaches to migration
A.
Examination of reasons for migration
B.
Examination of origin-destination patterns
C.
Consideration of whether or not boundaries were crossed, especially
boundaries between countries
III. Reasons for migration
A.
Two types of reasons: push factors and pull factors
B.
Push factors are factors that make you want to leave your origin
1.
E.g., lack of work, lack of land, famine, persecution of various sorts,
crummy climate
C.
Pull factors are factors that attract you to your destination
1.
E.g., a job, demand for your skills, good climate, more congenial
cultural climate, available land, being captured and forcibly taken to the
destination
a. Thomas theorem is alive and well in
migration: people move on the basis of what they think the destination will be
like, not on the basis of what it is actually like
D.
For most Americans, job-related reasons (push and pull) are the most
important reasons for moving, especially long moves
IV. Origin-Destination Patterns
A.
An important principle: at any time migration tends to be
concentrated in a limited number of origin-destination paths
1. Migration is not random or haphazard
2.
These paths are called streams
B. Important historical migrations
1.
Perhaps most important: movement from
2.
Also of importance for US: movement of 15 million slaves from
V. International vs internal
migration
A.
Governments get a lot more concerned about moves across national
boundaries than about other moves
VI. Migration Data
A.
We have good information about births and deaths, but lousy information
about migration
1.
One reason is that the agency that gathers statistics most directly, the
Immigration and Naturalization Service (INS), is also an enforcement agency, so
many immigrants have good reason to want to avoid them
VII. Important general facts about
migration
A.
Those most likely to move are young adults
B.
Men tend to make longer moves than women
C.
International migration is not "free." Countries erect
substantial barriers to migration in attempts to control the composition of
their population
VIII. Migration and the
A.
About 17 percent of Americans move every year
1.
Looked at another way, on average an American moves every 6 years
B.
Peak moving ages are 20-29
C.
Most moves, especially long distance moves, are for job-related reasons
D.
Migration to the
1.
High sex ratio
E.
Current legal migration to the
F.
Illegal migration to the