Economic values come in nominal and real forms. Nominal figures are measured at the prices of the day; real figures are adjusted for inflation so that changes reflect actual volume rather than rising prices. A nominal GDP that grows 5% while prices rise 4% reflects only about 1% real growth. For comparing output over time, real (inflation-adjusted, or constant-price) figures are usually the right choice.
Comparing economies across borders requires converting currencies, and there are two common methods. Market exchange rates convert at the rate currencies actually trade at, which is what matters for cross-border transactions. Purchasing-power parity (PPP) instead adjusts for differences in price levels — the fact that the same money buys more in some countries than others — and is often preferred for comparing living standards and real output.
The choice of method changes the ranking of economies. Lower-price-level countries tend to look larger under PPP than at market rates, because their output is valued at a common set of prices rather than at a possibly undervalued exchange rate. Neither method is simply correct; each answers a different question, so it is worth knowing which one a figure uses.
Most economic data is released with a lag and revised afterward. National accounts typically appear quarterly or annually, weeks or months after the period they cover, and early estimates are updated as more complete information arrives. Treat the most recent figures as provisional: a “first” GDP estimate can move meaningfully by the time it is final.