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2011-07-19 12:29:39
J. Welles Wilder is one of the most innovative minds in the field of technical
analysis. In 1978, he introduced the world to the indicators known as true
range and average true range as measures of volatility. Although they are used
less frequently than standard indicators by many technicians, these tools can
help a technician enter and exit trades, and should be looked at by all systems
traders as a way to help increase profitability.
What Is the Average True Range?
A stock's range is the difference between the high and low price on any given
day. It reveals information about how volatile a stock is. Large ranges
indicate high volatility and small ranges indicate low volatility. The range is
measured the same way for options and commodities - high minus low - as they
are for stocks.
One difference between stocks and commodity markets is that the major futures
exchanges attempt to prevent extremely erratic price moves by putting a ceiling
on the amount that a market can move in a single day. This is known as a lock
limit, and represents the maximum change in a commodity's price for one day.
During the 1970s, as inflation reached unprecedented levels, grains, pork
bellies and other commodities frequently experienced limit moves. On these
days, a bull market would open limit up and no further trading would occur. The
range proved to be an inadequate measure of volatility given the limit moves
and the daily range indicated there was extremely low volatility in markets
that were actually more volatile than they'd ever been.
Wilder was a futures trader at that time, when those markets were less orderly
than they are today. Opening gaps were a common occurrence and markets moved
limit up or limit down frequently. This made it difficult for him to implement
some of the systems he was developing. His idea was that high volatility would
follow periods of low volatility. This would form the basis of an intraday
trading system. (For related reading, see Using Historical Volatility To Gauge
Future Risk.)
As an example of how that could lead to profits, remember that high volatility
should occur after low volatility. We can find low volatility by comparing the
daily range to a 10-day moving average of the range. If today's range is less
than the 10-day average range, we can add the value of that range to the
opening price and buy a breakout.
When the stock or commodity breaks out of a narrow range, it is likely to
continue moving for some time in the direction of the breakout. The problem
with opening gaps is that they hide volatility when looking at the daily range.
If a commodity opens limit up, the range will be very small, and adding this
small value to the next day's open is likely to lead to frequent trading.
Because the volatility is likely to decrease after a limit move, it is actually
a time that traders might want to look for markets offering better trading
opportunities.
Calculating the Average True Range
The true range was developed by Wilder to address this problem by accounting
for the gap and more accurately measuring the daily volatility than was
possible by using the simple range calculation. True range is the largest value
found by solving the following three equations:
TR = H L
TR = H C.1
TR = C.1 L
Where:
TR represents the true range
H represents today's high
L represents today's low
C.1 represents yesterday's close
If the market has gapped higher, equation No.2 will accurately show the
volatility of the day as measured from the high to the previous close.
Subtracting the previous close from the day's low, as done in equation No.3,
will account for days that open with a gap down.
Average True Range
The average true range (ATR) is an exponential moving average of the true
range. Wilder used a 14-day ATR to explain the concept. Traders can use shorter
or longer timeframes based on their trading preferences. Longer timeframes will
be slower and will likely lead to fewer trading signals, while shorter
timeframes will increase trading activity. The TR and ATR indicators are shown
in Figure 1.
Figure 1: True range and average true range indicators
Figure 1 illustrates how spikes in the TR are followed by periods of time with
lower values for TR. The ATR smooths the data and makes it better suited to a
trading system. Using raw inputs for the true range would lead to erratic
signals.
Applying the Average True Range
Most traders agree that volatility shows clear cycles and relying on this
belief, ATR can be used to set up entry signals. ATR breakout systems are
commonly used by short-term traders to time entries. This system adds the ATR,
or a multiple of the ATR, to the next day's open and buys when prices move
above that level. Short trades are the opposite; the ATR or a multiple of the
ATR is subtracted from the open and entries occur when that level is broken.
The ATR breakout system can be used as a longer term system by entering at the
open following a day that closes above the close plus the ATR or below the
close minus the ATR.
The ideas behind the ATR can also be used to place stops for trading
strategies, and this strategy can work no matter what type of entry is used.
ATR forms the basis of the stops used in the famed "turtle" trading system.
Another example of stops using ATR is the "chandelier exit" developed by Chuck
LeBeau, which places a trailing stop from either the highest high of the trade
or the highest close of the trade. The distance from the high price to the
trailing stop is usually set at three ATRs. It is moved upward as the price
goes higher. Stops on long positions should never be lowered because that
defeats the purpose of having a stop in place. (For more, see A Logical Method
Of Stop Placement.)
Conclusion
The ATR is a versatile tool that helps traders measure volatility and can
provide entry and exit locations. An entire trading system can be built from
this single idea. It's an indicator that should be studied by serious market
students.
by Michael Carr, CMT
Mike Carr, CMT, is a member of the Market Technicians Association and editor of
the MTA's newsletter, Technically Speaking. He is a full-time trader and
writer.