What are the two main difficulties that arise in comparing different countries's GDP?

The two main difficulties in comparing different countries' GDP are differences in population size and variations in currency exchange rates. To account for population size, economists use GDP per capita, which divides the total GDP by the country's population to provide a more accurate representation of the standard of living. However, variations in currency exchange rates can also skew comparisons, since GDP is typically measured in a country's domestic currency and needs to be converted to a common currency. This issue is mitigated by using purchasing power parity (PPP) exchange rates, which adjust for price level differences between countries, providing a more consistent basis for comparison.