A two-sex renewal model and its population projection

Area of Science:

• Demography
• Mathematical Biology
• Population Dynamics

Background:

• Population projections commonly utilize one-sex renewal models.
• These models present biologically unrealistic scenarios, such as male mortality not influencing birth projections.

Purpose of the Study:

• Introduce a novel two-sex renewal model for population projections.
• Enhance the accuracy of demographic forecasting by incorporating both sexes in reproductive dynamics.

Main Methods:

• Developed a nonlinear two-sex renewal model.
• Defined joint age-specific birth rates for both sexes.
• Derived joint total fertility, net reproduction rate, and intrinsic growth rate.

Main Results:

• The two-sex model revealed a 14% underestimation of the intrinsic growth rate in Australia by one-sex models.
• One-sex models are biased, showing higher growth rates for low-fertility countries and lower rates for high-fertility countries compared to the two-sex model.
• Global population projections using the two-sex model indicate a smaller future world population.

Conclusions:

• The two-sex renewal model provides a more realistic and accurate approach to population projection.
• One-sex models are demonstrably biased and lead to significant projection errors.
• Adoption of the two-sex model is recommended for improved demographic forecasting worldwide.