Moving average,
what it is, how it is calculated, how you
can use it and its limitations
Here at
www.stocktradersbulletin.com
we will from time to time take a closer look at some of the tools
that is being used when doing technical analysis of stocks. We will
start by looking at something called moving average.
Moving average is a term
that is often being used when there is talk about stock- and forex-
trading, but what exactly is it and how can you use it if you do your
own analysis? You probably know how to calculate the average of a
pool of numbers but let us start with the basics.
Average-
and moving average- calculation
When you have a
series of numbers and you for some reason want the average of those
numbers you simply add all those numbers and divide the sum by how
many numbers you have. E.g. you have these five numbers: 8, 9, 10, 8
and 10. The sum of these numbers is 45.
Divide 45 by 5 and you get an average of 9.
If the five numbers listed
above were price data for company ZZZ we could say that last five
days average price for ZZZ is 9. Next day we read on the net that ZZZ
closed at 13. If we were to calculate the new five day’s average it
would become:
13 + 10 + 8 + 10 + 9 = 50
and five day average will now become 50 / 5 = 10 (Fig. 1). What we
have done here is to “move” the five day period one step forward
by including the latest close and excluding the now sixth day close
thereby creating what we call a moving average. This procedure is
repeated for every new day so that we will get a series of moving
average numbers that we can plot as a line in our charts.
Fig. 1. Five day
average calculation.
Plotting moving average
When doing technical
analysis we analyze charts where price and other data are plotted. To
be able to get something useful from moving average we should plot
the data in our charts together with the price curve (Fig. 2). In
figure 2 you see price data plotted along
price and volume (light blue bars). On top of the price bars we have
plotted a five day moving average as a dark blue line. Taking a
closer look at this line we see that it is smoother than the actual
price movement. If we were to plot a longer moving average using e.g.
50 days moving average we would see an even much more smoothed curve
as the value plotted for a specific day is the average of the number
of days we have used in the calculation for the moving average.

Fig.
2. Plotting of a five day moving average. The blue line seen in this
chart is the five day moving average of the price for this stock.
Types of moving average
The moving average
we have talked about in this article so far
is what we call a simple moving average. There are many other types
of moving averages as well but the most common one beside simple
moving average is exponential moving average. When applying
exponential moving average, last days values are being weighted
thereby making last days movements “more important”. The result
of this is that the graph will react quicker to the price changes
that occur. In Figure 3 we have plotted two moving averages. The blue
line is a 20 day simple moving average and the green line is a 20 day
exponential moving average. It is easy to see that there is a
difference between the two lines. Even though it is the same number
of days that is being used in the calculation of the moving averages
we see that the green line (exponential moving average) is following
the price development a bit more closely than the more smoothed blue
line.
We earlier
said that we plot moving average along with price data, but it is
also important to remember that moving averages can be applied on all
kinds of data and not just on price data. Other examples could be
moving average of volume and relative strength index to mention a
few.

Fig. 3. Plotting of 20
days simple moving average (blue line) and 20 days exponential
moving average (green line). We see that the green line react more
to the price changes that occur than the blue line.
A basic moving average
trading system
To see how a moving
average trading system could be used we will now design a very basic
moving average trading system consisting of two moving averages. The
coding and plotting of data shown here is done in a software called
Amibroker (www.amibroker.com)
which is a technical analysis software where you can plot data,
program trading systems, optimize- and test- your own trading ideas.
In this example we
will use a short 5 day simple moving average and a medium long 25 day
simple moving average to form the framework for our trading system.
What we want to do next is to design our trading system to buy the
stock when the 5 day moving average crosses above the 25 day moving
average and sell when the 5 day moving average crosses below the 25
day moving average. The coding done to make this system is seen in
figure 4.

Fig. 4. Amibroker code
for the moving average trading system.
When we plot these
two moving averages we see why we want to buy the stock when 5 day
moving average crosses above the 25 day moving average and sell when
the opposite occur. Basically what we want is to be on the “right”
side as the stock price moves upwards or downwards (Fig. 5).

Fig. 5. We want to own
stocks in this company when the blue line is higher than the green
line, and sell (or short) the stock when the blue line falls below
the green line. The light blue bars seen in the lower part of the
chart is the trading volume for the different days.
From the plot it looks
like this system is quite promising with regard to being profitable
but to make sure that it is actually profitable we need to do some
more testing. What we want is a trading system that will perform well
over time and in all kinds of market situations. Although the trading
system seems promising at a first glance the testing of this system
shows something else. As seen from the test report produced by
Amibroker the system performance was rather poor over the test period
from mid June 2004 to mid June 2008. With a win percent of 33.3 this
is probably a trading system that we should leave and not trade as is
today. Although the trading system does not perform as wanted the
overall idea for the system might still be something to build further
upon (Fig. 6).
Fig. 6. Profit
distribution for our trading system. We see that we have a few nice
returns of investment here but when we just have a few winners we
choose not to go further with this system. What we want is a much
more even profit distribution that could be e.g. 20 winners in the
5% to 10% range rather than one winner of 100%. Only then can we say
that we have a more robust trading system.
It has to be said
that the testing done here is very simple and
www.stocktradersbulletin.com
will look deeper into testing of trading systems in an article at a
later stage. Also it should be noted that the testing here was done
on one stock which is not a good enough foundation for validating
trading systems.
Conclusion
Moving average is a tool
that could be used in a meaningful way if it is applied correctly.
From our analysis in
the previous section we can say that using moving average alone for
your trading will probably not give you the profit you would like to
see in the long run. You will simply see too many false signals for
when to buy and sell. To minimize the false signals you should use
moving average in conjunction with other technical analysis tools.
What tools and how you want to do that is entirely up to you but what
you should remember to do if you have the chance is to test, test and
test your system and make sure that you are not just seeing wishful
things before you go ahead and do actual trading with real money.
Final note
What you have read
here is just one method of how you could use a moving average. As we
have seen the method presented in this article is not a very
profitable one but the intention here is to give you some information
about moving average and possibly also give you some inspiration from
where you can continue with your own ideas and development of trading
systems. For more information about trading systems please read our
article “Building a trading system” found in our article section
at www.stocktradersbulletin.com.