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Market timing is the strategy of making buy or sell decisions of financial assets (often stocks) by attempting to predict future market price movements. The prediction may be based on an outlook of market or economic conditions resulting from technical or fundamental analysis. This is an investment strategy based on the outlook for an aggregate market, rather than for a particular financial asset.
Moving average 
Market timing often looks at various moving averages. Popular are the 50- and 200-day moving averages. Some people believe that if the market has gone above the 50- or 200-day average that should be considered bullish, or below conversely bearish. Technical analysts consider it significant when one moving average crosses over another. The market timers then predict that the trend will, more likely than not, continue in the future. Others say, "nobody knows" and that world economies and stock markets are of such complexity that market timing strategies are unlikely to be more profitable than buy-and-hold strategies.
Differing views on the viability of market timing 
Whether market timing is ever a viable investment strategy is controversial. Some may consider market timing to be a form of gambling based on pure chance, because they do not believe in undervalued or overvalued markets. The efficient-market hypothesis claims that financial prices always exhibit random walk behavior and thus cannot be predicted with consistency.
Some consider market timing to be sensible in certain situations, such as an apparent bubble. However, because the economy is a complex system that contains many factors, even at times of significant market optimism or pessimism, it remains difficult, if not impossible, to pre-determine the local maximum or minimum of future prices with any precision; a so-called bubble can last for many years before prices collapse. Likewise, a crash can persist for extended periods; stocks that appear to be "cheap" at a glance, can often become much cheaper afterwards, before then either rebounding at some time in the future or heading toward bankruptcy.
Proponents of market timing counter that market timing is just another name for trading. They argue that "attempting to predict future market price movements" is what all traders do, regardless of whether they trade individual stocks or collections of stocks, aka, mutual funds. Thus if market timing is not a viable investment strategy, the proponents say, then neither is any of the trading on the various stock exchanges. Those who disagree with this view usually advocate a buy-and-hold strategy with periodic "rebalancing".
Brokerages may favor institutional investors at the expense of smaller retail investors 
Perhaps consistent with these two opposing views is that, as with any type of trading, market timing is difficult to carry out on a consistent basis, particularly for the individual investor unschooled in technical analysis. Retail brokers are also generally unschooled in both the mind set and the tools needed to successfully time the market, and indeed most are actively discouraged by the brokerages themselves from moving their clients in and out of the market. However, as market makers, many of these same brokerages take the opposite approach with their large institutional clients, trading various financial instruments for these clients in an attempt to "predict future market price movements" and thereby make a profit for the institutions. This dichotomy in the treatment of institutional vs. retail clients can potentially be controversial for the brokerages. It may suggest for example that retail brokers and their clients are discouraged from market timing, not because it doesn't work, but because it would interfere with the brokerages' market maker trading for their institutional clients. In other words, retail clients are encouraged to buy and hold so as to maintain market liquidity for the institutional trading. If true, this would suggest a conflict of interest, in which the brokerages are willing to sacrifice potential returns for the smaller retail clients in order to benefit larger institutional clients.
The 2008 decline in the markets is instructive. While many retail brokers were instructed by their brokerages to tell their clients not to sell, but instead "look to the long term", the market makers at those same brokerages were busy selling to cash to avoid losses for the brokerages' large institutional clients. The result was that the retail clients were left with huge losses while the institutions fled to the safety of short term bonds and money market funds, thereby avoiding similar losses.
Curve fitting and over-optimization 
A major stumbling block for many market timers is the phenomenon of curve fitting. This means that a given set of trading rules has been over-optimized to fit the particular dataset for which it has been back-tested. Unfortunately, if the trading rules are over-optimized they often fail to work on future data. Market timers attempt to avoid these difficulties in a number of ways. One is by looking for clusters of parameter values which work particularly well. Another is using out-of-sample data, which ostensibly allows the market timer to see how the system will work on unforeseen data. However, critics charge that once the strategy has been revised to reflect such data it is no longer "out-of-sample".
Independent review of market-timing services 
Several independent organizations (e.g., Timer Digest and Hulbert Financial Digest) have tracked some market timers' performance for over thirty years. These organizations have found that purported market timers in many cases do no better than chance, or even worse. However, there are exceptions, with some market timers over the thirty-year period having performances that substantially and reliably exceed those of the general stock market or the sectors in which the market timers invest. Jim Simons' Renaissance Technologies Medallion Hedge Fund has consistently outperformed the market. The fund allegedly uses mathematical models developed by Elwyn Berlekamp.
A recent study suggested that the best predictor of a fund's consistent outperformance of the market was low expenses and low turnover, not pursuit of a value or contrarian strategy. However, other studies have concluded that some simple strategies will outperform the overall market. One market-timing strategy is referred to as Time Zone Arbitrage.
Evidence against market timing 
Mutual fund flows are published by organizations such as Investment Company Institute and TrimTabs. These show that flows generally track the overall level of the market. For example, in the beginning of the 2000s decade, the largest inflows to stock mutual funds were in early 2000 while the largest outflows were in mid-2002. It is good to note that these mutual fund flows were near the start of a significant bear (downtrending) market and bull (uptrending) market respectively. A similar pattern is repeated near the end of the decade.
This mutual fund flow data seems to indicate that most investors (despite what they may say) actually follow a buy high, sell low strategy. Studies confirm that the general tendency of investors is to buy after a stock or mutual fund price has already increased. This creates a surge in the number of buyers which then drives the price even higher. However, eventually, the supply of buyers becomes exhausted, and the demand (supply and demand) for the stock declines and the stock or fund price also declines.
The famous Dalbar study found that the average investor's return in stocks is much less than the amount that would have been obtained by simply holding an index fund consisting of all stocks contained in the S&P 500 index. A similar conclusion is drawn in the recent study by Valeriy Zakamulin.
A recent study suggests that corporations and investment banks cannot time the credit markets. They show that investment banks such as Goldman Sachs do as poorly as firms like Ford when it comes to timing the issuance of their bonds.
While market timing is legal, the Financial Industry Regulatory Authority has long frowned on the practice since it passes the trading costs to long-term investors. Consequently, many brokerages will not fill market-timing orders.
What some financial advisors say 
Financial advisors often agree that investors have poor timing, becoming less risk averse when markets are high and more risk averse when markets are low. This is consistent with recency bias and seems contrary to the acrophobia explanation. "The only problem is that, unlike Mr. Spock of Star Trek fame, humans are not entirely rational beings."
Proponents of the efficient-market hypothesis claim that prices reflect all available information. EMH assumes that investors are highly intelligent and perfectly rational. However, others dispute this assumption. "Of course, we know stocks don't work that way." In particular, proponents of behavioral finance claim that investors are irrational but their biases are consistent and predictable.
See also 
- Using the 200-day moving average
- Pruitt, George, & Hill, John R. Building Winning Trading Systems with TradeStation(TM), Hoboken, N.J: John Wiley & Sons, Inc. ISBN 0-471-21569-4, p. 106-108.
- Finance and Business
- Malkiel B.G. (2004) Can predictable patterns in market returns be exploited using real money? Journal of Portfolio Management, 31 (Special Issue), p.131-141.
- Shen, P. Market timing strategies that worked — based on the E/P ratio of the S&P 500 and interest rates. Journal of Portfolio Management, 29, p.57-68.
- Global Equity Strategy
- Bad Timing Eats Away at Investor Returns
- Worldwide Mutual Fund Assets and Flows, Fourth Quarter 2008
- You Should Have Timed the Market on finance.yahoo.com
- Investors Flee Stock Funds
- If You Think Worst Is Over, Take Benjamin Graham's Advice
- Dumb money: Mutual fund flows and the cross-section of stock returns
- Fact Sheet: Morningstar Investor Return
- Black Swans, Portfolio Theory and Market Timing
- Fooled by Data-Mining: The Real-Life Performance of Market Timing with Moving Averages
- Frank, M., P. Nezafat, Credit Market Timing
- Switching to Cash May Feel Safe, but Risks Remain
- WHY INVESTORS DON’T BEAT THE MARKET
- Jim Cramer's Getting Back to Even, pp. 63-64