A1: In macro-economics one studies the economy as a whole, trying to understand how the various parts interact, how they fit together and how a change in one part of the economy will affect another. These "parts" that one analyses do not exist in reality - they are theoretical constructs that are abstract concepts similar to concepts such as "intelligence" or "emotions" - though they cannot be observed in reality we have designed methods of making these abstractions more real by means of measurement.