What is Preston Curve?

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?