The most common and most likely answer to this crossword clue is the 10 letter word MONETARISM
I've seen this crossword clue in The Daily Telegraph
M
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More clues leading to the result MONETARISM
Buddy explains!

The straight part
We know that "economic theory" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case economic theory = monetarism.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MONETARISM mean?
MONETARISM noun- The doctrine that economic systems are controlled by variations in the supply of money.
- The political doctrine that a nation's economy can be controlled by regulating the money supply.