POPULATION

The Demographic Transition Model

Do Now:

Define and provide a formula for each of the following:

• CRUDE BIRTH RATE (CBR)

• CRUDE DEATH RATE (CDR)

• RATE OF NATURAL INCREASE (RNI, NIR)

Crude Birth Rate

This is an annual statistic that measures the number of infants born for every 1,000 members of a population.

Formula:

LIVE BIRTHS POPULATION ÷ 1,000

What is considered high or low?

Ranges of Crude Birth Rate

Limitation:

Only a portion of the 1,000 people are women who are able to bear children.

• High = 18-50

• Low = 8-17

Crude Death Rate

This is an annual statistic that measures the number of deaths for every 1,000 members of the population.

Formula:

DEATHS POPULATION ÷ 1,000

What is considered high?

Ranges of Crude Death Rate

High death rates usually indicate a country that is

experiencing war, disease, or famine.

High = 20-50

Remember that this is a yearly statistic that may change based on environmental or social factors.

What is the NIR or RNI (Natural Increase Rate) and how is it calculated?

Natural Increase Rate (NIR, RNI)

• This statistic compares the CBR with the CDR to calculate the rate of a population’s increase (positive number) or decrease (negative number).

• Formula:

Birth Rate – Death Rate %

10

Why do you have to divide by 10?

When would this number be negative?

What does this formula NOT include in calculating population change?

Doubling Time

• The formula for doubling time (Td) in a population with an NIR of r% is based on logarithms:

Td = log (2) ~ 70

log (1 + r/100) r

Why is this number only an estimate?

How can we factor in migration?

Net Migration Rate Formula

• This is an annual statistic.• To factor in migration, take the number of immigrants per 1,000

members of the population minus the number of emigrants per 1,000 members of the population.

• Formula:

Number of immigrants - Number of emigrants Population ÷ 1,000 Population ÷ 1,000

How can we combine this migration statistic with the rates of birth and death to determine the growth of a given population in a particular year?

The Demographic Equation

The demographic equation calculates the rate of a population’s growth in a particular year based on migration, birth, and death statistics:

(Birth Rate – Death Rate) + Net Migration Rate %10

Why do you have to divide by 10?Why could this number be negative?

What is the TOTAL FERTILITY RATE?

Total Fertility Rate

In addition to CBR, geographers also use the Total Fertility Rate to measure the number of births in a society

This number is NOT an annual statistic. It is an estimate based on fertility over the prior 30 years.

Number of Children Born Women Aged 15-45

Can this number be negative?

Natural Rate of Increase vs.

Total Fertility Rate

Remember the car analogy:

When TFR = 2.1, you have hit the brakes. The rate of population growth decreases.

When RNI = 0 (Birth Rate = Death Rate), car has stopped; the population stops growing altogether.

If the RNI is negative (Birth Rate < Death Rate), the car is rolling backwards; the population is shrinking.