The Preston curve refers to a certain empirical relationship that is witnessed between life expectancy and per capita income in a country.
It was first proposed by American sociologist Samuel H. Preston in 1975.
He authored a paper titled “The changing relation between mortality and level of economic development”.
He found that people living in richer countries generally had longer life spans when compared with people living in poorer countries.
This is likely because people in wealthier countries have better access to healthcare, are better educated, live in cleaner surroundings, enjoy better nutrition etc.
The average per capita income of Indians rose from around ₹9,000 per year in 1947 to around ₹55,000 per year in 2011.
During the same period, the average life expectancy of Indians rose from a mere 32 years to over 66 years.
However, the positive relationship between per capita income and life expectancy begins to flatten out after a certain point.