Population Growth and Population Projections. Birth Intervals. Post partum ovulation time to conceive birth Amenorrhea conception. Menarche. Marriage. 1 st Birth. 2 nd Birth. 3 rd Birth. Issues Events out of order (births then marry) IVF
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Post partum ovulation time to conceive birth
Total number of daughters born
between 15 and 49 that takes
into account survival of mothers.
Lx refers to number of person years lived by a cohort of women
fx refers to the age – specific fertility rate
Assumes additions/deletions happen once a year
Population Growth Rates in Urban and Rural Areas, Less and More Developed Countries, 1975 to 2000 and 2000 to 2025. Derived from United Nations, World Urbanization Prospects: The 1999 Revision (2000).
Assumes additions/deletions happen throughout the year
.07 or 7% so 70/7 means a population doubling in 10 years
Many developed countries have very low growth rates and, as a result, the equation shows doubling times of hundreds or thousands of years. But these countries are not expected to ever double again. Most, in fact, likely have population declines in their future.
Many less developed countries have high growth rates that are associated with short doubling times, but are expected to grow more slowly as birth rates are expected to continue to decline
1 billion in 1804
2 billion in 1927 (123 years later)
3 billion in 1960 (33 years later)
4 billion in 1974 (14 years later)
5 billion in 1987 (13 years later)
6 billion in 1999 (12 years later)
Objective: Calculate Ax
Objective: Calculate b, crude birth rate, in a stable population
Objective: Calculate population x+1/2 years ago
The number of births in a stable population that occurred x + 1/2 years ago is simply the crude birth rate b (which does not change) times the population x + 1/2 years ago.
Now, not all those people survived – need to calculate proportion survived to age x:
(Number born x+1/2 years ago) x (survived at age x+1/2) tells you how many people there will be at age x today in a stable population
Implies perpetual growth or ultimate extinction
Assumes there are upper and lower bounds to population size
GO TO EXCEL
Last line is specified as a regression and can be estimated as one
GO TO EXCEL
Equations 1 and 2 show m(ale) superscripts; comparable equations for females
Around the year 2000, the population began to generate "negative momentum": a tendency to decline owing to shrinking cohorts of young people that was brought on by low fertility (birthrate) over the past three decades.
Currently, the effect of negative momentum on future population is small. However, each additional decade that fertility remains at its present low level will imply a further decline in the European Union (EU) of 25 to 40 million people, in the absence of offsetting effects from immigration or rising life expectancy.
The tendency for population growth to continue beyond the time that replacement-level fertility has been achieved because of a relatively high concentration of people in the childbearing years.
For example, the absolute numbers of people in developing countries will continue to increase over the next several decades even as the rates of population growth will decline. This phenomenon is due to past high fertility rates which results in a large number of young people. As these youth grow older and move through reproductive ages, the greater number of births will exceed the number of deaths in the older populations
Projection methods and assumptions. The alternative population projections were carried out using standard cohort component population projection methods using software developed by the authors. Since this analysis aims at isolating the impacts of alternative fertility assumptions, in all scenarios only the fertility component was modified as described in Table 1, while we assumed that mortality stayed constant at life expectancies of 81.5 years for women and 75.5 years for men. We also assumed a closed population without migration.