Understanding Population Pyramids: Analysis and Key Factors
Analyzing Sex Structure
To comment on the sex structure, one must:
- Find the numerical superiority of males at birth by calculating the sex ratio or looking at the longer bar at the bottom of the pyramid (0-4 years) on the side of men.
- Indicate when the higher male mortality leads to equalization of the effect of both sexes.
- Note the disparity in effect for the elderly.
- Explain the longer life expectancy of women and the causes of higher male mortality (war, lifestyle, etc.).
Analyzing Age Structure
Identify and comment on the age structure from:
- The percentage of young people (0-14 years), adults (15-64 years), or elderly (65 years and over).
- The form of the pyramid: triangular, bell, or urn.
Triangular or Parasol Shape
A triangular or parasol shape (e.g., Spain in 1900) indicates a young population. Young people represent over 35% of the population, and the elderly less than 5%. The base is wide, indicating high birth rates, and the population decreases rapidly towards the top due to high mortality rates and low life expectancy. Identify the causes of high fertility and high mortality, and the consequences of the high percentage of young people (e.g., strong demand for jobs in a backward economy, high unemployment, and emigration).
Bell Shape
A bell shape (e.g., Spain in 1970) indicates an adult or stationary population. The base is less broad because the birth rate has been cut, albeit mildly, so it still allows for generational change. The population slowly decreases towards the top due to low mortality rates. There is a buildup of adults and not very high percentages of young people (between 25% and 35%) or elderly (between 5% and 12%). Indicate the causes of the progressive cutting of birth rates and low mortality, and the consequences of the predominance of an adult population (many assets, not too many dependents).
Urn Shape
An urn shape (e.g., Spain in 2000) indicates an aging population. The base narrows due to low and declining birth rates. The percentage of elderly is high (over 12%) due to increased life expectancy. Explain the causes of aging and its consequences (e.g., problems related to pensions, health, and welfare).
Analyzing Significant Demographic Events
Comment on the most significant demographic events deduced from the incoming and outgoing profile of the pyramid (always starting from the top).
Starters (Indentations)
Starters indicate a loss of population. They are due to under-natality or increased mortality due to wars, famines, or epidemics. They can also be due to emigration. Keep in mind that the starters produced by the dead of war never coincide with the years of war but are between 20 and 30 years before (4-5-6 bars above the pyramid), affecting all the male population at the time the war was of fighting age (20-30 years). The entrees that match the war years are due to under-natality produced by it and affect almost equally men and women. The incoming of a pyramid are a “hollow” or “small” generation, which is reflected below 20-30 years, creating a new entrant or a reduction in effect when the members of this generation reach the age to marry and have children (20-30 years) and are less numerous than a generation, the total of their children is also lower.
Projections (Bulges)
Projections of the pyramid indicate a population increase. They are due to several causes: post-war baby boom, economic development, immigration, etc. They cause a “large” generation below 20-30 years; when they reach the age to marry and have children, as are the total number of children is also higher.
To analyze the incoming and outgoing of a pyramid, you have to relate the historical events that have demographic incidence, using the chronological axis with dates of birth for each age group.