Population Pyramids: Structure and Sex Differences in Demographics

Understanding Population Pyramid Structure

The two histogram bars are arranged horizontally, typically along the X-axis (abscissa). Conventionally, the bars on the left indicate the age groups of males, and those on the right represent the female population.

The Y-axis (ordinate) identifies the groups of age, usually in five-year intervals (e.g., 0–4, 5–9, 10–14, etc.). The bar representing the lowest age group is placed at the bottom of the chart, with ages gradually increasing towards the top.

When detailed information is available (such as births and deaths per year), the population pyramid can be drawn with corresponding annual details (bars representing year-to-year data). The scale of the X-axis typically represents absolute values (i.e., the number of inhabitants in each age group and sex).

This type of plot takes its name from the characteristic pyramid shape observed in societies with high birth rates, resulting in a broad base. The shape gradually narrows due to increasing and cumulative mortality as the population ages.

Key Demographic Characteristics by Sex and Age

The biological characteristics of the human species create consistent, slight differences in population distribution by sex across different ages:

1. Higher Birth Rate for Males

More boys than girls are born. This fact is general and consistent across the demographics of virtually every country in the world. However, the difference is relatively small (typically less than 2%) but consistent. As a result, the bars at the base of an age pyramid are almost always greater for the male population (except in very small populations or highly specialized cases).

2. Elevated Male Mortality Rates

Male mortality is always higher than female mortality at all ages, especially in the early stages of life, concerning both neonatal mortality and infant mortality (under one year old).

Consequently, in an age and sex pyramid for a country with low migration, the extent of the bars tends to be similar as we ascend through the ages, reaching a point beyond which the bars representing the female population become noticeably broader.

3. Female Longevity and Life Expectancy

Life expectancy is always higher in women, often by several years, depending largely on the level of socio-economic development of the country. This inherent feature of the human species largely explains the significant gap observed between the sexes in older age groups.