### Author Topic: Standard deviation  (Read 515 times)

#### marc-antony foreman

• Newbie
• • Posts: 2
• Karma: +0/-0 ##### Standard deviation
« on: October 13, 2021, 06:04:27 am »
Hello, does the standard deviation moving average match the  moving average of the ratio?

For example if I select EMA for the ratio, does the standard deviation use the EMA as well or does it use SMA for that caclulation.

Thanks

• Sr. Member
•     • • Posts: 305
• Karma: +12/-0 ##### Re: Standard deviation
« Reply #1 on: October 13, 2021, 06:19:14 am »
From the documentation of ratio model:

* we trade pair of stocks A, B, having price series A(t), B(t)
* we need to calculate ratio time series R(t) = A(t) / B(t)
* let's apply moving average of type T with period Pm on R(t) to get time series M(t)
* let's apply standard deviation with period Ps on R(t) to get time series S(t)
* now we can create Z-score series Z(t) as Z(t) = (R(t) - M(t)) / S(t), this time series can give us z-score to signal trading
* decision directly (in reality we have two Z-scores: Z-scoreask and Z-scorebid as they are calculated using different prices, but for the sake of simplicity let's now pretend we don't pay bid-ask spread and we have just one Z-score)

About your question about the MA type - nope we always use SMA for underlying MA calculation in stddev.