Final answer:
Social epidemiology is the study of how health and illness are distributed and influenced by socio-demographic factors, revealing disparities between high-income and low-income nations.
Step-by-step explanation:
The study of how health and illness vary by socio-demographic characteristics is called social epidemiology. This field investigates the causes and distribution of diseases and how they are affected by social factors. For example, high-income nations tend to face health issues related to obesity, such as heart disease and diabetes, while low-income nations often grapple with infectious diseases and high infant mortality rates. Social epidemiology also explores the impact of social problems on the health of different populations, revealing disparities based on socio-economic status, geographic location, and access to healthcare.