Calculating market size by starting with a broad industry macro-estimate from a research firm (like Gartner or Forrester) and filtering it down.
Why it matters: While often used in early pitch decks, it is generally considered less rigorous than bottom-up sizing and often overstates realistic market potential.
In practice: Stating 'The global AI market is $500B, and we are targeting the healthcare segment which is 10%, so our market is $50B.'