The Overbought/Oversold ("OB/OS") indicator is a
market breadth indicator based on the smoothed difference between
advancing and declining issues.
Interpretation
The OB/OS indicator shows when the stock market is
overbought (and a correction is due) and when it is oversold (and a
rally is due).
Readings above +200 are generally considered bearish
and readings below -200 are generally considered bullish. When the OB/OS
indicator falls below +200 a sell signal is generated. Similarly, a buy
signal is generated when the OB/OS indicator rises above -200.
As with all OB/OS-type indicators, extreme readings
may be a sign of a change in investor expectations and may not be
followed by the expected correction. (Refer to the discussion on the
Advance/Decline Ratio, and the McClellan Oscillator, for additional
comments on extremely overbought/oversold conditions.)
Example
The following chart shows the DJIA and the
Overbought/Oversold indicator.
I drew "buy" and "sell" arrows when the indicator
penetrated the +200/-200 levels. The OB/OS indicator works very well in
this type of trading-range market.
Calculation
The Overbought/Oversold indicator is a 10-period
exponential moving average of the difference between the number of
advancing and declining issues.