The bull/bear ratio is just one piece of the puzzle. It’s a sentiment indicator. Search the term and you’ll find some good definitions.

As for using the ratio to invest, when the bulls are getting pessimistic and down on the market, they’re feeling the effects of a bad market. The tide will eventually turn, and it’s probably wise to start buying some.

As I said, it’s one piece. I’d use the charts and technical analysis to get the primary read and use this ratio as a secondary tool.