Demography: Populations and their Description



Summary for Chapter 3, Demography: Populations and their Description

These notes are intended to clarify Chapter 3, not replace it. The text covers all test material.

The most basic population indicators are the crude birth rate (CBR) and the crude death rate (CDR), reported in births (or deaths) per thousand people. These can be used to calculate the natural increase rate (equation 1). The NIR can be used to approximate calculating the doubling time (equation 2). They are a first estimate of population growth (figure 1). This does not tell us age distributions, or what ages most deaths occur. You don’t need to memorize this, but it is nice to know how to calculate this basic information.

|Natural increase rate (NIR) = ( CBR – CDR) /10 |(equation 1) |

|Doubling time in years = log(2) / log(1+NIR) |(equation 2) |

[pic]Figure 1: NIR and population growth.

|Table 1: Example population statistics and estimates |

|Country |Stage |CBR ** |CDR ** |NIR *** |Life expectancy|Doubling |

| |* | | | | |time *** |

|Somalia |2 |42.7 |14.9 |2.8% |50.4 years |26 years |

|Kenya |2 |33.5 |8.9 |2.5% |59.4 years |29 years |

|India |2(3 |21 |7.5 |1.35% |66.8 years |52 years |

|U.S.A. |3(4 |13.8 |8.4 |0.54% |79.8 years |128 yrs |

|Italy |5 |9.18 |9.84 |-0.28% |81.8 years |1049 yrs |

| | | | | | |**** |

|Japan |5 |7.3 |10.1 |-0.28% |82.2 years |247 yrs ****|

|Source: CIA World Factbook |

| * my |

|estimate, ** births (or deaths) per 1000 people, *** calculated **** halving time|

|(population / 2) |

More detail can be gathered using the average life expectancy at birth, (table 1) and a population pyramid (figure 2). The pyramid shows the population age and sex distribution. If the population is stable, the pyramid shows at what age people die. However, this does not work in practice because populations are dynamic. War, disease, famine, economic crises, cultural conflict or change, and political upheavals make future populations hard to estimate, and it is often useful to study how the pyramids change over time by looking their change over time, and studying the social and epidemiological factors that influence births and deaths. The US Census Bureau and the CIA have wonderful resources for this. (See and )

[pic]

Figure 2: Population pyramids for three demographic stages. (Source: Pearson Education, Inc.) Kenya appears to be transitioning from higher birth rates to lower birth rates (stage 2 moving to 3) while the U.S. is in Stage 4, (low birth and death rates, close to ZPG), and Italy is stage 5 (low birth and lower death rates, population decline). (Stage 1 is only in isolated groups, without access to health care, safe water or sanitation.)

One long term pattern of population change is called the demographic transition. This is a general pattern of population growth and decline that is a response to changes in culture which affect birth and death rates (Table 2). In demographic stage 1, high death rates caused by diseases are offset by high birth rates. In demographic stage 2, the death rate drops some due to basic improvements in cleanliness, cleaner water supply, better sanitation, and pest control. Demographic stage 3 is a delayed response to the increased life expectancy; fewer people die, so fewer children are eventually desired. Also, increased medical care further suppresses the death rate in demographic stage 3. In demographic stage 4, the death rate levels off as most people die of old age diseases. The birth rate also drops to match the death rate, largely because of other cultural changes. (These include transition to a manufacturing and services based economy, increased female education and literacy, higher costs of raising children, and shifts from traditional to modern society cultural norms.) In demographic stage 5, the birth rate continues to drop, and negative population growth (NIR < 0) results (figure 1).

[pic]

Figure 3: The demographic transition. Stage 5 (not shown) has low death rates and even lower birth rates. In demographic stage 1, pandemics drive death rates. In stage 2, sanitation and basic health care reduce pandemics, but changes in birth rates lag death rates by 2 or 3 generations. In stage 3, death rates are driven down by medicine, and birth rates start to respond to less demand for children (more live). In stage 4, birth rates approximately equal death rates, while in stage 5, the birth rate falls below the low death rate. (University of Michigan, )

The difference between the birth rate and death rate (figure 3) results in a natural increase rate estimate (equation 2). This drives migration patterns over time, as new farmland becomes scarce. This economic migration drive often leads people from stage 2 and 3 countries with insufficient jobs to move to stage 3, 4, or 5 countries which have transitioned to manufacturing and service sector economies. Demographic stage 5 countries are particularly promising destinations, as there are fewer local people due to the negative NIR. In previous times, populations migrated to new lands, and experienced relative isolation, resulting in cultural diversity. However, the globalization of transportation has increased the mixing of people and cultures, increasing both cultural variety and conflict within many regions.

Population change is directly tied to (historical) cultural changes, including advances in sanitation, cleanliness, medical care, and water supplies needed to support cities. Historically, cities had to deal with these problems to avoid becoming places to avoid. In the Dark Ages, cities were more hazardous, and death rates were higher there than in the countryside. (Plagues were often found first in cities along the trade routes from China, including the Silk Road and maritime trade routes.) This is in contrast with well developed cities, such as Rome (which had better aqueducts, sewers, public baths, etc.) and modern cities, with added medical care facilities.

Demographic regions focus on the present state of various parameters, including CBR, CDR, NIR, TFR, and population density. Maps of the present state of affairs do not usually show changes in state, any state transition cause(s). For example, in demographic stage 5 countries, the death rates are high because the population is aging, while in many LDCs, death rates are high because of diseases, civil wars, starvation, etc.

[pic][pic]

Figure 4: Death rates. This shows effects but not causes. In some more developed countries, (MDCs), low birth rates and large elderly populations produce higher death rates. In many less developed countries (LDCs), high death rates are driven by diseases, malnutrition, warfare, and genocide. Local research is necessary to clarify root causes. (See text for CBR, NIR, &) (Source: )

Demographic change involves studying change in population patterns, including changes in CBR, CDR, TRF, life expectancy and other variables. These changes, along with economic and other cultural factors, drive migration, another form of demographic change. The changes are often associated with cultural changes at a site (e.g. more or less health care, food, clean water, cultural clash), and the situation, or relative position of other places (sites), which have their own characteristics. These characteristics push people from one place and pull them to another, and the push/pull factors are broadly categorized as economic, cultural, and lifestyle factors. Distance costs and cultural differences often limit long-range migration, which is often driven by need.

|Push/pull factor ( |Economic (work needs) |Cultural (persecution, freedom) |Lifestyle (choices) |

|International migration |Need job, land to farm |Escape persecution, conflict |(presently less common) |

|Interregional migration |Disaster, need job, farm |Escape local conflict |Climate, retirement |

|Intraregional migration |(usually lifestyle) |(presently less common) |Close to work, amenities, climate |

Table 1: Migration push and pull factors, pushing from source locations, pulling to destinations.

Demographic Ecology focuses on population interactions with ecosystems. This includes environmental disease vectors affecting humans. It also includes human effects on the environment, driven by population density and human activities. These can severely degrade the environment. Likewise, living or working in a location with natural hazards puts populations at risk.

Demographic interaction focuses on effects of the mix of cultures, and effects on other cultural aspects. It includes responses of local cultures to migrations, and the effects of population growth on traditional and popular cultures, including religious and political institutions. These institutions also affect population growth, affecting abortion, birth control, sexual norms, marriage, etc. Interactions often vary markedly between cultures.

Demographic Landscape focuses on effects of populations on the landscape. I discussed this in more general terms of population growth and consumption effects on the landscape (e.g. food and resources). The book has more specific examples of this process, and has greater depth. (Use the book as a font of knowledge.)

Bibliography:

US Census,

CIA World Factbook,

Jordan-Bychkov, Terry G., Mona Domosh, Roderick P. Neumann, Patricia L. Price. 2012. Fundamentals of the Human Mosaic. W. H. Freeman and Company, NY, NY. 357 pp.

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