|
Answer |
Exponential moving averages are by nature "cumulative"
indicators, in that, regardless of the period you specify, their values
are based in some part on EVERY prior bar in the data that is loaded.
The general formula for the exponential moving average follows: EMA =
EMA.1 + (PRICE - EMA.1 ) * (2 / (n + 1) )
n = period
Notice how the EMA value for each bar is built using the EMA value
from the previous bar. The EMA continues to build upon itself.
EMA does not have a specific period of data which it uses to compute
it's value. A 20 period Simple Moving Average is always looking
just at the last 20 bars, and taking their average. A 20 period
Exponential Moving average however is based in some part of all the
previous data. The key here is how much data is loaded for the
calculation? How much is Investor/RT loading? How much are your other
sources loading? Logically, the more data you load, the more likely your
values are to match up with other sources.
In Investor/RT, if you're looking at a daily chart with the EMA in it,
then the number of bars used to compute the value of EMA is going to
depend on the "Viewing Period" of your chart. For an EMA, I might
suggest loading a number of bars at least twice your period. So for a
200 EMA, I would try a viewing period of "Last 2 Years" or so.
Now, if you're running a scan, which I suspect you may be, or if you're
using EMA in a custom column, then Investor/RT is going to do it's best
to compute a desired number of bars that need to be loaded for the
computation to occur. In general, for cumulative type indicators,
this number is going to be equal to the period plus 80 (a 200-period EMA
would load 280 bars). The user can however override this number with his
own number. In the Scan setup window (or the Custom Indicator or Signal
setup windows), in the lower right hand corner, is a "Bars:" setting
that will default to "Automatic". If your values aren't matching up, and
you suspect it could be because your indicator is "cumulative", try
using a larger number here.
You can also click the "Check" button in the Scan setup window, and
Investor/RT will tell you how many bars are going to be requested
(loaded) for this scan, along with how many bars are required.
The easiest way to identify a cumulative indicator is to check if it
involves any of these smoothing (moving average) types:
- Exponential
- Welles Wilder
- Adaptive
Some "cumulative" indicators would include:
- RSI (Only when Morris Modified is UNCHECKED)
- ADXR
- ADX
- DI+/DI-
- Fisher Transform
- TRIX
- And any indicator using one of the smoothing methods mentioned
above.
|