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# how to calculate population growth rate

From Wikipedia

Birth rate

Crude birth rate is the nativity or childbirths per 1,000 people per year (in estimation review points).

According to the United Nations' World Population Prospects: The 2008 Revision Population Database, crude birth rate is the number of births over a given period divided by the person-years lived by the population over that period. It is expressed as number of births per 1,000 population. CBR = (births in a period / population of person-years over that period).

Another indicator of fertility that is frequently used is the total fertility rate, which is the average number of children born to each woman over the course of her life. In general, the total fertility rate is a better indicator of (current) fertility rates because, unlike the crude birth rate, it is not affected by the age distribution of the population. Fertility rates tend to be higher in less economically developed countries and lower in more economically developed countries.

The birth rate is an item of concern and policy for a number of national governments. Some, including those of Italy and Malaysia, seek to increase the national birth rate using measures such as financial incentives or provision of support services to new mothers. Conversely, other countries have policies to reduce the birth rate, for example, China's one child policy. Measures such as improved information about and availability of birth control have achieved similar results in countries such as Iran.

There has also been discussion on whether bringing women into the forefront of development initiatives will lead to a decline in birth rates. In some places, government policies have been focused on reducing birth rates through improving women's sexual and reproductive health and rights. Typically, high birth rates has been associated with health impairments and low life expectancy, low living standards, low status of women, and low levels of education. There are claims that as countries go through economic development and social change, population growth such as birth rate declines.

In 1974, at the World Population Conference in Bucharest, women's issues gained considerable attention. Family programmes were seriously discussed and 137 countries drafted a World Population Plan of Action. In the discussion, many countries accepted modern birth control, such as the pill and the condom, but opposed abortion. In 1994, another action plan was drafted in Cairo under the United Nations. They discussed the concern on population and the need to incorporate women into the discourse. They agreed that improvements in women's status, and initiatives in defense of reproductive health and freedom, the environment, and sustainable socio-economic development were needed.

Generally, birth rate is calculated using live birth counts from a universal system of registration of births, deaths, and marriages, and population counts from a census or using estimation through specialized demographic techniques. Birth rate is also commonly used to calculate population growth. It is combined with death rates and migration rates to calculate population growth.

As of 2009, the average birth rate for the whole world is 19.95 per year per 1000 total population, a 0.48% decline from 2003's world birth rate of 20.43 per 1000 total population. According to the CIA - The World Factbook, the country with the highest birth rate currently is Niger at 51.26 births per 1000 people. The country with the lowest birth rate is Japan at 7.64 births per 1000 people. (Hong Kong, a Special Administrative Region of China, is at 7.42 births per 1000 people.) As compared to the 1950s (birth rate was at 36 births per 1000 in the 1950s), birth rate has declined by 16 births per 1000 people.

Birth rates ranging from 10-20 births per 1000 are considered low, while rates from 40-50 births per 1000 are considered high. There are problems associated with both an extremely high birth rate and an extremely low birth rate. High birth rates can cause stress on the government welfare and family programs to support a youthful population. Additional problems faced by a country with a high birth rate include educating a growing number of children, creating jobs for these children when they enter the workforce, and dealing with the environmental effects that a large population can produce. Low birth rates can put stress on the government to provide adequate senior welfare systems and also the stress on families to support the elders themselves. There will be less children or working age population to support the constantly growing aging population.

## Methods of measuring birth rate

The crude birth rate is the number of births in a given population during a given time period (such as January 1 - December 31) divided by the total population and multiplied by one thousand.

## Birth rate and the Demographic Transition Model

The Demographic Transition Model describes how population mortality and fertility decline as social and economic development occurs through time. The two major factors in the Demographic Transition Model are Crude Birth Rate (CBR) and Crude Death Rate (CDR). There are four stages to the Demographic Model. In the first and second stages, CBR remains high because people are still in agrarian cultures and need more labour to work on farms. In addition, the chances of children dying are high because medicine is not as advanced during that phase. In the third stage, CBR starts to decline due to women's increasing participation in society and the reduced need for families to have many children to work on farms. In the fourth stage, CBR is sustained at a very low level, with some countries having rates that are below replacement levels in other countries.

Question:if a populations growth rate is 0.02 and its population is 100,000,000 how large will the population be in 5 years? show your calculations

Answers:You need to assume exponential growth. P(t) = A * exp(rt) A = 100 000 000 r = 0.02 t = 5 P(5) = 110 517 092

Question:my problem is about the population of geese in a pond. at t=25 weeks, the population is 20.6 and the max number of geese the pond can hold is 42. is the rate of growth increasing or decreasing?

Answers:You haven't given us any information about the goose population or how it's changing. You've simply given us the population at one point, and the maximum number of geese the lake can hold. That's not enough to go on. An inflection point is nothing more than where the 2nd derivative changes sign. At such a point, the population could be increasing or decreasing, or reaching a max or a min. Just telling us that it's an inflection point doesn't tell us what's happening to the function or its 1st derivative. Since the pond can hold more geese, all we know is that it could be increasing, but not that it actually is increasing.

Question:Given that the world population in 2009 is 6.78 billion people, calculate the projected population in 2058 assuming growth rates of 1%, 1.4% and 2%.

Answers:Use the formula 6.78 *(1+g)^T where g is the growth rate, T is the number of years to go (50). For g=1% I find 11.15 billion. You do the others.

Question:Is there a formula that could answer this question :if there are 6 billion people on earth and population doubles every 30 years - can we find how many years has it taken to get to our current population?

Answers:yes we can. but it will be inacurate because. population growth r is assumed as constant however r is a function of a lot of observed and non observed parameters.the followings are few observed factors. - birth rate and death rate - male/female in general and in each age category - availability of water, food - war, plague , disasters - sexual activity and orientation