Context: The Preston curve gives a positive empirical relationship between a country’s life expectancy and its per capita income. It was first identified by Samuel H. Preston in 1975.

• It suggests that as poor countries grow and their per capita income increases, life expectancy rises significantly due to better access to healthcare, education, nutrition, and living conditions. However, this relationship flattens out at higher income levels, indicating diminishing returns on life expectancy gains with further income increases.

About the Preston Curve

• About: The Preston Curve is a graph that shows the relationship between the average income per person in a country (usually measured as GDP per capita) and the average life expectancy of its people.

• Origin: The concept was introduced by American sociologist Samuel H. Preston in his 1975 paper titled “The changing relation between mortality and level of economic development”.

Key Observations of the Preston Curve

• i) Generally, people in wealthier countries live longer compared to those in poorer countries.

• ii) This trend is likely because individuals in richer nations typically have better access to healthcare, education, clean environments, and nutritious food.

• iii) Economic Growth and Life Expectancy: When a country’s economy grows and incomes rise, life expectancy also tends to increase significantly. This improvement is initially due to better access to basic necessities like food and healthcare.

• Example: In India, the average income rose from approximately Rs 9,000 per year in 1947 to about Rs 55,000 in 2011. Correspondingly, the average life expectancy increased from 32 years to over 66 years during the same period.

• Limitations of Income Growth on Life Expectancy: The relationship between per capita income and life expectancy starts to plateau beyond a certain point. Further increases in income do not lead to significant gains in life expectancy, possibly because there is a natural limit to human lifespan.

Shift in Preston curve 

• An increase in the per capita income of a country does not cause much of a rise in the life expectancy of its population beyond a point, perhaps because human life span cannot be increased indefinitely.

Problems in the Curve 

• Higher life expectancy has been achieved by countries even at low per capita income levels due to improvements in medical technology, such as the development of life-saving vaccines.

• Thus, improvement in life expectancy can hold true as a result of public investment in human development like better education & healthcare.

Significance 

• Other development indicators such as infant and maternal mortality, education, healthcare, etc. also improve when the per capita income of a country rises.

• The rapid economic growth of India and China over the last few decades, which has helped improve life expectancy and other development indicators, has been cited as an example of faster economic growth leading to better development outcomes.