Oscillators generate buy and sell signals in various ways. Some signals are geared towards early entry, while others appear after the trend has begun. In addition to buy and sell signals, oscillators can signal that something is amiss with the current trend or that the current trend is about to change. Even though oscillators can generate their own signals, it is important to use these signals in conjunction with other aspects of technical analysis. Most oscillators are momentum indicators and only reflect one characteristic of a security's price action. Volume, price patterns and support/resistance levels should also be taken into consideration.
Positive and Negative Divergences
Divergence is a key concept behind many signals for oscillators as well as other indicators. Divergences can serve as a warning that the trend is about to change or set up a buy or sell signal. There are two types of divergences: positive and negative. In its most basic form, a negative divergence is when an indicator declines while the underlying security advances. A positive divergence is when the indicator advances while the underlying security declines.
A negative divergence occurs when the underlying security moves to a new high, but the indicator fails to record a new high and forms a lower high. For momentum indicators, a negative divergence shows slowing upside momentum that can sometimes foreshadow a bearish reversal. Not all negative divergences result in good signals, especially during a strong uptrend. On the Staples (SPLS) chart above, the stock formed a higher high in September, but the MACD did not exceed its prior high. A negative divergence formed and the MACD soon moved below its signal line (red).
A positive divergence occurs when a security moves to a new low, but the indicator holds above its prior low to form a higher low. For momentum indicators, a positive divergence shows less downside momentum that can sometimes foreshadow a bullish reversal. Not all positive divergences result in good signals, especially in a strong downtrend. On the Sprint (S) chart above, the stock formed a lower low in early September, but RSI held above its prior low to form a positive divergence. Also, notice that RSI was oversold in mid-August and held above 30 in September. The subsequent move above 50 in RSI and the breakout in Sprint confirmed the signal. Sprint later moved back below its breakout and warranted a reassessment at that time.
Divergences, both positive and negative, can also form in non-momentum indicators like On Balance Volume, the Accumulation Distribution Line, the AD Line and Chaikin Money Flow. On the Expeditors (EXPD) chart above, the stock moved to a new high in September, but On Balance Volume (OBV) did not confirm with a higher high. A lower high is forming in OBV and the indicator moved below its 10-day SMA.
Overbought and Oversold Extremes
Banded oscillators are designed to identify overbought and oversold extremes. Since these oscillators fluctuate between extremes, they can be difficult to use in trending markets. Banded oscillators are best used in trading ranges or with securities that are not trending. In a strong trend, users may see many signals that are not really valid. If a stock is in a strong uptrend, buying on oversold conditions will work much better than selling on overbought conditions.
In a strong trend, oscillator signals against the direction of the underlying trend are less robust than those with the trend. The trend is your friend and it can be dangerous to fight it. Even though securities develop trends, they also fluctuate within those trends. If a stock is in a strong uptrend, buying when oscillators reach oversold conditions (and near support tests) will work much better than selling on overbought conditions. During a strong downtrend, selling when oscillators reach overbought conditions would work much better. If the path of least resistance is up (down), then acting on only bullish (bearish) signals would be in harmony with the trend. Attempts to trade against the trend carry added risk.
When the trend is strong, banded oscillators can remain near overbought or oversold levels for extended periods. An overbought condition does not indicate that it is time to sell, nor does an oversold condition indicate that it is time to buy. In a strong uptrend, an oscillator can reach an overbought condition and remain so as the underlying security continues to advance. A negative divergence may form, but a bearish signal against the uptrend should be considered suspect. In a strong downtrend, an oscillator can reach an oversold condition and remain so as the underlying security continues to decline.