To calculate the bullish percent for an index, it's a very simple equation: Number of stocks on P&F buy signals/total number of stocks in the index. So a BPI reading of 0.00, such as in the gold miners index currently, indicates that not a single company is on a buy signal. Even when the index contains a small number of stocks, 30 or less like the gold miners index, it's still extremely rare for none of them to have a buy signal. Think about that for a minute - one would suspect that there might be unique, company-specific factors (ie. a new discovery, takeover rumors, etc) that would place at least one company on a buy signal...right? I believe the chart above bears that out.
Over the last 7 years, (1500 trading days) the GMBPI it has registered 0.00 only five times, and today is one of those days. So what does this mean? Well, the GMBPI is a contrary indicator. From www.stockcharts.com, "In its most basic form, the Bullish Percent Index favors the bulls when above 50% and the bears when below 50%. The bulls have the edge when over 50% of stocks are on a P&F buy signal. BPI is also considered overbought when above 70% and oversold when below 30%."
By this definition, gold miners are insanely oversold. Can they continue to remain oversold? Of course. But once you've hit rock bottom, there's nowhere to go but up.