Breadth Advance-Decline Line

The Advance-Decline Line measures the amount of advancing stocks minus the amount of declining stocks. It is a leading indicator for the stock market.

For example:
When a lot of stocks in an index go down, while the index itself goes up, it means that the move up was the result of a select group of large companies that were going up, while most of the stocks in that index went down. This is a bearish indicator and the Advance-Decline Line will go down.

Here are some charts and it seems that the NASDAQ is the most bearish and NYSE is the most bullish.

NYSE:

NASDAQ 100:

Dow Jones:

S&P 500: