Preston Curve

• The Preston Curve is a graphical representation that illustrates the relationship between a country’s per capita income and its life expectancy.
  • Proposed by: American sociologist Samuel H. Preston in 1975.
  • Purpose: To show how improvements in income relate to improvements in health outcomes, particularly life expectancy.

Understanding the Curve

• The graph plots:
  • X-axis: Per capita income (usually measured in USD or PPP-adjusted).
  • Y-axis: Life expectancy at birth (in years).
• At lower levels of income, even small increases in income lead to significant improvements in life expectancy. 
• However, beyond a certain income threshold, further increases in income lead to diminishing returns in life expectancy.

Two Phases of the Curve

Steep Curve (Low-Income Countries):

• At very low income levels, countries experience large gains in life expectancy due to:
• Better nutrition
• Improved sanitation
• Basic healthcare access
• Public health interventions (e.g., vaccines, clean water)

Flattening Curve (High-Income Countries):

• As income grows beyond a threshold (approx. $10,000–$15,000 per capita):
• Gains in life expectancy slow down
• Lifestyle diseases (like obesity, stress, pollution) may counteract further improvements
• Health becomes more influenced by behavioural, environmental, and social factors than income alone.

Significance for Policy Makers

• Income growth alone is not sufficient.
  • Beyond a point, non-income factors (like education, environment and preventive healthcare) matter more.
• Governments should focus on:
  • Improving healthcare access
  • Reducing inequality
  • Ensuring clean air, water, and sanitation
  • Promoting healthy lifestyles
• Helps in designing inclusive growth policies:
  • Economic growth must be accompanied by investments in human development.

Relevance to India

• India has seen steady growth in per capita income, especially after liberalization (1991).
• However, life expectancy (around 70 years) has not increased at the same rate due to:
  • Air and water pollution
  • Poor healthcare infrastructure
  • Nutritional deficiencies
  • Unequal access to services
• Thus, India is possibly on the flattening segment of the Preston Curve.