If price movements are choppy and erratic over an extended period of time, then a moving average is probably not the best choice for analysis. The chart for MMM shows a security that moved from 70 to 90 in a few weeks in late April. Prior to this advance, the price gyrated above and below its moving average. After the advance, the stock continued its erratic behavior without developing much of a trend. Trying to analyze this security based on a moving average is likely to be a lesson in futility.

A quick look at the chart for AOL shows a different picture than for MMM. Over the same time period, AOL has shown the ability to trend. There are 3 distinct trends or price movements that extend for a number of months. Once the stock moves above or below the 70-day SMA, it usually continues in that direction for a little while longer. MMM, on the other hand, broke above and below its 70-day SMA numerous times and would have been prone to numerous whipsaws. A longer moving average would probably work better for MMM, but it is clear that there are fewer characteristics of trend than in AOL.
Moving Average Settings
Once a security has been deemed to have enough characteristics of trend, the next task will be to select the number of moving average periods and type of moving average. The number of periods used in a moving average will vary according to the security’s volatility, trendiness and personal preferences. The more volatility there is, the more smoothing that will be required and hence the longer the moving average. Stocks that do not exhibit strong characteristics of trend may also require longer moving averages. There is no one set length, but some of the more popular lengths include 21, 50, 89, 150 and 200 days as well as 10, 30 and 40 weeks. Short-term traders may look for evidence of 2-3 week trends with a 21-day moving average, while longer-term investors may look for evidence of 3-4 month trends with a 40-week moving average. Trial and error is usually the best means for finding the best length. Examine how the moving average fits with the price data. If there are too many breaks, lengthen the moving average to decrease its sensitivity. If the moving average is slow to react, shorten the moving average to increase its sensitivity. In addition, you may want to try using both simple and exponential moving averages. Exponential moving averages are usually best
for short-term situations that require a responsive moving average. Simple moving averages work well for longer-term situations that do not require a lot of sensitivity.
Uses for Moving Averages
There are many uses for moving averages, but three basic uses stand out:
Trend identification/confirmation
Support and Resistance level identification/confirmation
Trading Systems
Trend Identification/ConfirmationThere are three ways to identify the direction of the trend with moving averages: direction, location and crossovers.
The first trend identification technique uses the direction of the moving average to determine the trend. If the moving average is rising, the trend is considered up. If the moving average is declining, the trend is considered down. The direction of a moving average can be determined simply by looking at a plot of the moving average or by applying an indicator to the moving average. In either case, we would not want to act
on every subtle change, but rather look at general directional movement and changes.
In the case of Disney, a 100-day exponential moving average (EMA) has been used to determine the trend. We do not want to act on every little change in the moving average, but rather significant upturns and downturns. This is not a scientific study, but a number of significant turning points can be spotted just based on visual observation
(red circles). A few good signals were rendered, but also a few whipsaws and late signals. Much of the performance would depend on your entry and exit points. The length of the moving average influences the number of signals and their timeliness. Moving averages are lagging indicators. Therefore, the longer the moving average is,
the further behind the price movement it will be. For quicker signals, a 50-day EMA could have been used.
The second technique for trend identification is price location. The location of the price relative to the moving average can be used to determine the basic trend. If the price is above the moving average, the trend is considered up. If the price is below the moving average, the trend is considered down.
This example is pretty straightforward. The long-term for ENE is determined by the location of the stock relative to its 100-day SMA. When ENE is above its 100-day SMA, the trend is considered bullish. When the stock is below the 100-day SMA, the trend is considered bearish. Buy and sell signals are generated by crosses above and below themoving average. There was a brief sell signal generated in Aug-98 and a false buy
signal in Nov-99. Both of these signals occurred when Enron’s trend began to weaken. For the most part though, this simple method would have kept an investor in throughout most of the bull move.
The third technique for trend identification is based on the location of the shorter moving average relative to the longer moving average. If the shorter moving average is above the longer moving average, the trend is considered up. If the shorter moving average is below the longer moving average, the trend is considered down.
Support and Resistance Levels
Another use of moving averages is to identify support and resistance levels. This is usually accomplished with one moving average and is based on historical precedent. As with trend identification, support and resistance level identification through moving averages works best in trending markets.