Population Pyramids A Population Pyramid is two backto-back bar graphs. One side of the graph shows the number of males while the other side shows females in a particular population in five-year age groups. These age groups are also called COHORTS. Thus, a Population Pyramid is AGE and SEX DISTRIBUTION within a country. A pyramid graphically displays long term trends in the birth and death rates, as well as shorter term impacts such as baby-booms, wars and epidemics. Population Pyramids “How it works” Bar graphs are a handy way to illustrate numbers. Graphing the number of males and females in Canada for various age groups according to the 1961 Census, the result would be the two figures. The top figure is % males in Canada’s total population, while the bottom figure is % females. Population Pyramids “How it works”…2 Displaying these two graphs together, horizontally and as a mirror image, a Population Pyramid is made. This figure shows the 1961 Population Pyramid for Canada. In this period, Canada’s population is growing. Interpretation of this pyramid. It narrows toward the top. The death rate is higher among older people than among younger people. There are not as many people in their 20s as in their 30s. The people in their 20s in 1961 were born at the end of the Depression and the start of WWII. This was a time of economic hardship and uncertainty. People were having fewer children in this period. In 1961, the pyramid had a wide base. Adding the percentages for the three lowest age cohorts, we learn that 35% of the population was under 15. These are the “baby boomers,” a large group of people born between 1947 and 1966 when the economy was growing and prospering. Population Pyramids Population Pyramids CONSTRUCTION The X-axis illustrates males and females. Males are always shown on the left and females on the right. The Y-axis is age cohorts Males and females can be represented or measured by the absolute number OR as a percentage of the total population. Population Pyramids Types of Pyramids Expansive — A broad base indicating a high proportion of children, a rapid rate of population growth, and a low proportion of older people. Stable growth — A structure with indentations that even out and reflect slow growth over a period. Stationary — A narrow base and roughly equal numbers in each age group, tapering off at the older ages. This pyramid shows an unchanging pattern of fertility and mortality. Declining — A high proportion of aged persons and declining numbers. Population Pyramids The triangular distribution is also be called a pyramid or exponential distribution. In this example, the wide base indicates a large number of children, while the rapid narrowing shows that many people die between each age band. The pyramid shows a population with a high birth rate, a high death rate and a short life expectancy. This pattern is typical of less economically developed countries. Here, there may be little access and incentive to use birth control, poor environmental factors (e.g., lack of clean water) and limited access to health services. Population Pyramids Rapid Growth The triangle shape suggest rapid population growth. Population Pyramids Slow Growth The square-like structure is slow growth. The lump in the pyramid between the ages of about 35 to 50 is the post-World War II "baby boom." As this population ages and climbs up the pyramid, there will be a much greater demand for medical and other geriatric services. Population Pyramids Negative Growth The population is shrinking due to a low birth rate and a stable death rate. Increased emigration may also be a contributor to a declining population. Population Pyramids The following data are age cohorts for different countries of the world. Build a Population Pyramid for each country and describe the growth pattern. Males Females 0-19 20-39 40-59 60+ 0-19 20-39 40-59 60+ Canada 13 15 14 7 12 15 14 9 Kenya 28 15 5 2 27 15 5 2 Germany 11 15 14 10 10 14 13 14 Pakistan 27 15 7 2 25 14 7 2 Poland 14 15 13 7 14 14 14 10 Population Pyramids The figures illustrate four different patterns or characteristics of population growth. For each figure, describe the pattern (e.g., high birth rate, high death rate) and the type of pyramid (e.g., Expansive, Stationary).