What is Preston Curve?

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About Preston Curve:

It is a graphical representation that shows the relationship between a country’s per capita income (usually measured as GDP per capita) and its average life expectancy.
It was first proposed by American sociologist Samuel H. Preston in his 1975 paper, “The changing relation between mortality and level of economic development”.
Preston 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.
When a poor country begins to grow, its per capita income rises and causes a significant increase in life expectancy initially as people are able to consume more than just subsistence calories, enjoy better healthcare, etc.
For example, 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.
In other words, 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.

Q1: What is Gross domestic product (GDP)?

GDP is the total monetary or market value of all the finished goods and services produced within a country’s borders in a specific time period. As a broad measure of overall domestic production, it functions as a comprehensive scorecard of a given country’s economic health.

Source: What does the Preston curve postulate?