How has global classification of countries shifted throughout the past 50 years?

Answer

To fully answer this question, we need to clarify the classification system we are analyzing. Assuming we are looking at the World Bank's income classification system, we can find historical data for each country's income classification over the past 50 years on the World Bank's website.

Q: What classification system are we referring to? A: It is unclear from the question, we need to clarify which classification system we are analyzing.
Q: Assuming we are referring to the World Bank's income classification system, what are its categories? A: The classifications are low income, lower-middle income, upper-middle income, and high income.
Q: Can we find historical data for each country's classification? A: Yes, the World Bank provides historical data for each country's income classification over time.
Q: Can we access this data online? A: Yes, the World Bank's website provides access to this data.