Higher Highs and Lower Lows

I have heard that one of the strongest leading indicators is when the S&P500 creates a higher high and a lower low than the previous month, it tells you that a change in the overall direction is in the wings.

Here are the monthly closes since 1999. It definitely holds during this brief time period

http://finance.yahoo.com/q/hp?s=SPY&a=00&b=29&c=1999&d=03&e=3&f=2009&g=m&z=66&y=66