What Is The Relative Strength Index – RSI?
The relative strength index (RSI) is a momentum indicator that measures the magnitude of recent price changes to evaluate overbought or oversold conditions in the price of a stock or other asset. The RSI is displayed as an oscillator (a line graph that moves between two extremes) and can have a reading from 0 to 100. The indicator was originally developed by J. Welles Wilder Jr. and introduced in his seminal 1978 book, New Concepts in Technical Trading Systems.
Another trading technique examines the RSI’s behavior when it is re-emerging from overbought or oversold territory. This signal is called a bullish “swing rejection” and has four parts:
- RSI falls into oversold territory.
- RSI crosses back above 30%.
- RSI forms another dip without crossing back into oversold territory.
- RSI then breaks its most recent high.
As you can see in the following chart, the RSI indicator was oversold, broke up through 30% and formed the rejection low that triggered the signal when it bounced higher. Using the RSI in this way is very similar to drawing trendlines on a price chart.
Like divergences, there is a bearish version of the swing rejection signal that looks like a mirror image of the bullish version. A bearish swing rejection also has four parts:
- RSI rises into overbought territory.
- RSI crosses back below 70%.
- RSI forms another high without crossing back into overbought territory.
- RSI then breaks its most recent low.
The Difference Between RSI and MACD
The Moving Average Convergence Divergence (MACD) is another trend-following momentum indicator that shows the relationship between two moving averages of a security’s price. The MACD is calculated by subtracting the 26-period Exponential Moving Average (EMA) from the 12-period EMA. The result of that calculation is the MACD line. A nine-day EMA of the MACD, called the “signal line,” is then plotted on top of the MACD line, which can function as a trigger for buy and sell signals. Traders may buy the security when the MACD crosses above its signal line and sell, or short, the security when the MACD crosses below the signal line.
The RSI aims to indicate whether a market is considered to be overbought or oversold in relation to recent price levels. The RSI calculates average price gains and losses over a given period of time; the default time period is 14 periods with values bounded from 0 to 100.
The MACD measures the relationship between two EMAs, while the RSI measures price change in relation to recent price highs and lows. These two indicators are often used together to provide analysts a more complete technical picture of a market.
These indicators both measure momentum in a market, but because they measure different factors, they sometimes give contrary indications. For example, the RSI may show a reading above 70 for a sustained period of time, indicating a market is overextended to the buy side in relation to recent prices, while the MACD indicates the market is still increasing in buying momentum. Either indicator may signal an upcoming trend change by showing divergence from price (price continues higher while the indicator turns lower, or vice versa).
Limitations Of The RSI
The RSI compares bullish and bearish price momentum and displays the results in an oscillator that can be placed alongside a price chart. Like most technical indicators, its signals are most reliable when they conform to the long-term trend. True reversal signals are rare and can be difficult to separate from false alarms. A false positive, for example, would be a bullish crossover followed by a sudden decline in a stock. A false negative would be a situation where there is bearish crossover, yet the stock accelerated suddenly upwards.
Since the indicator displays momentum, as long as ab asset’s price momentum remains strong (either up or down) the indicator can stay in overbought or oversold territory for long periods of time. Therefore, the RSI is most trustworthy in an oscillating market when the price is alternating between bullish and bearish periods.
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