There are several traditional and modern ways to measure a country's level of development. Traditionally, development was equated with economic growth and countries were classified based on their Gross National Product per capita. However, GNP has limitations and does not reflect differences in cost of living between countries. More modern measures include Purchasing Power Parity per capita, energy consumption, percentage of the workforce in different sectors, and quality of life indices like the Human Development Index which considers education, income, and health. Collecting accurate social and demographic data to measure development can be challenging for various reasons.