Absolute Breadth Index (ABI)

ABI is |advances − declines|: how one-sided the day was, ignoring direction. High readings mean the market moved as one block (everything up or everything down); low readings mean an even, mixed tape.

Persistently high ABI marks macro-driven regimes — correlation ≈ 1 days cluster in crashes and manias. Low-ABI stretches are the stock-picker phases where individual assets trade on their own stories.