The idea behind the indicator is that more stocks will advance than decline in bull markets and vice-versa in bear markets. Generally, markets are considered oversold when the oscillator is below -100, and overbought when it is above +100.
The McClellan oscillator is not a stand-alone indicator. It measures the trend strength of advancing and declining issues, and not necessarily market turns. Leadership in a handful of stocks has characterized many bull markets, defying the premise that the broad market must advance for stock indexes to hit new highs.
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