The Money Flow Index (MFI) is an oscillator that uses both price and volume to measure buying and selling pressure. Created by Gene Quong and Avrum Soudack, MFI is also known as volume-weighted RSI. MFI starts with the typical price for each period. Money flow is positive when the typical price rises (buying pressure) and negative when the typical price declines (selling pressure). A ratio of positive and negative money flow is then plugged into an RSI formula to create an oscillator that moves between zero and one hundred. As a momentum oscillator tied to volume, the Money Flow Index (MFI) is best suited to identify reversals and price extremes with a variety of signals.
As a volume-weighted version of RSI, the Money Flow Index (MFI) can be interpreted similar to RSI. The big difference is, of course, volume. Because volume is added to the mix, the Money Flow Index will act a little differently than RSI. Theories suggest that volume leads prices. RSI is a momentum oscillator that already leads prices. Incorporating volume can increase this lead time.
Quong and Soudack identified three basic signals using the Money Flow Index. First, chartists can look for overbought or oversold levels to warn of unsustainable price extremes. Second, bullish and bearish divergence can be used to anticipate trend reversals. Third, failure swings at 80 or 20 can also be used to identify potential price reversals. For this article, the divergences and failure swings are be combined to create one signal group and increase robustness.
Overbought and oversold levels can be used to identify unsustainable price extremes. Typically, MFI above 80 is considered overbought and MFI below 20 is considered oversold. Strong trends can present a problem for these classic overbought and oversold levels. MFI can become overbought (>80) and prices can simply continue higher when the uptrend is strong. Conversely, MFI can become oversold (<20) and prices can simply continue lower when the downtrend is strong. Quong and Soudack recommended expanding these extremes to further qualify signals. A move above 90 is truly overbought and a move below 10 is truly oversold. Moves above 90 and below 10 are rare occurrences that suggest a price move is unsustainable. Admittedly, many stocks will trade for a long time without reaching the 90/10 extremes. However, chartists can use the StockCharts.com scan engine to find those that do. Links to such scans are provided at the end of this article.
01oversold
JB Hunt (JBHT) became oversold when the Money Flow Index moved below 10 in late October 2009 and early February 2010. The preceding declines were sharp enough to produce these readings, but the oversold extremes suggested that these declines were unsustainable. Oversold levels alone are not reason enough to turn bullish. Some sort of reversal or upturn is needed to confirm that prices have indeed turned a corner. JBHT confirmed the first oversold reading with a gap and trendline break on good volume. The stock confirmed the second oversold reading with a resistance breakout on good volume
02overbought
Aeropostale (ARO) became overbought when the Money Flow Index moved above 90 in late September and late December 2009. Extremes in MFI suggested that these advances were unsustainable and a pullback was imminent. The first overbought reading led to a sizable decline, but the second did not. Notice that ARO peaked with the first overbought reading and formed lower highs into October. The late October support break signaled a clear trend reversal. After the December overbought reading, ARO moved above 23 and consolidated. There were two down gaps and a support break, but these did not hold. Price action was stronger than the overbought reading. ARO ultimately broke resistance at 24 and surged back above 28. The second signal did not work.
via stockcharts.com
