Population - More Than Just a Number


A Population is a total of all the organisms of the same group or species, which live in a particular geographical area, and are capable of interbreeding.

Population Dynamics

There are many factors that whould be considered when studying a population. These include birth rates, death rates, mobility, age distribution and density.

Birth Rates

Fertility Rates indicate the level of births per year per 1,000 women of child bearing age. Statistics are usualy focused on the fmale 15 to 44 year old age group with particular emphasis is placed on the 20 to 34 year old age group due to its heightened fertility rate. In the United States, the most common source of fertility data will come from the Center for Disease Control (CDC) and the Departments of Health for State level data.

Birth Rates Graph
Birth Rates Graph

Death Rates

Death rates are expressed in number of deaths per year per 100,000 population. For example, in 2013, according to the Center for Disease Control, the United States death rate was 821.5 per 100,000 population.

Mobility Rates

Mobility Rates determine the number of people moving in or out of a particular geographic area. It indicates the level of population change due to migration or immigration. The US Census Bureau releases annual statistics that display the geographic origination of people moving. These statistics are broken down into moves within the same county, different county in the same state, different state or moves made from outside the US. The population of movers is further grouped by age to give further depth to the statistics. For example, the largest number of movers in 2013 by age was the 20-24 year old group. This would be expected since there are a large number of people transitionsing from school to their first career-oriented job.

Age Distributions

The distribution of a population by age groups is an important set of statistics to determine all of the goods, services and government programs that are needed in a geographic area. The US Census Bureau releases the population of each year's age groups divided by one year increments for its Decennial Census every decade. 2010 was the last Decennial Census. For each year in between Decennial Census releases, age groups are divided into five year increments (i.e. 0-4 year olds, 5-9 year olds, 10-14 year olds etc.). The figures also are segmented between the male and female populations.

The study of age groups in a population can be very useful in locating or moving a business, determining the apropriate level of government programs and school facilities and the placement of housing developments. There are generational age groups, such as the "Baby Boomers" (born in the 18 year period following World War II (1946-1964)) that are widely followed by those who study demographics. Another important age group are the "Echo Boomers" that are often referred to as "Millennials" or "Generation Y". This age group consists of children have primarily Baby Boomer parents and were born from 1981 to 1995 according to Demographic Challenges and Opportunities for U.S. Housing Markets (Bipartisan Policy Center March 2012).

Age Distribution Graph with Male and Female Distributions
Age Distribution Graph with Male and Female Distributions

Population Density

Population Density measures the population per measured area within a specified geography. It is usually expressed in persons per square mile or persons per square kilometer. Only square mileage (kilometers) that contain land mass are included in the calculation. For example, according to the US Census Bureau, there were 87.4 people per square mile in the United States in 2010.

Population Density per Square Mile
Population Density per Square Mile

Population Growth Statistics

Population Growth Statistics are an important component in the examination of population. Percentage growth over varying time frames can be useful to determine the characteristics of population growth. In addition, current growth rates can be extended into future years to extrapolate projected growth in future years.

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