# Standard Deviation (volatility)

Standard Deviation of price over a rolling lookback window. Also known as Historical Volatility (HV). Z-Score is also returned. [Discuss]

```
// usage
IEnumerable<StdDevResult> results =
quotes.GetStdDev(lookbackPeriods);
// usage with optional SMA of SD (shown above)
IEnumerable<StdDevResult> results =
quotes.GetStdDev(lookbackPeriods, smaPeriods);
```

## Parameters

`lookbackPeriods`

* int* - Number of periods (

`N`

) in the lookback period. Must be greater than 1 to calculate; however we suggest a larger period for statistically appropriate sample size.`smaPeriods`

* int* - Optional. Number of periods in the moving average of

`StdDev`

. Must be greater than 0, if specified.### Historical quotes requirements

You must have at least `N`

periods of `quotes`

to cover the warmup periods.

`quotes`

is a collection of generic `TQuote`

historical price quotes. It should have a consistent frequency (day, hour, minute, etc). See the Guide for more information.

## Response

```
IEnumerable<StdDevResult>
```

- This method returns a time series of all available indicator values for the
`quotes`

provided. - It always returns the same number of elements as there are in the historical quotes.
- It does not return a single incremental indicator value.
- The first
`N-1`

periods will have`null`

values since there’s not enough data to calculate.

### StdDevResult

`Date`

* DateTime* - Date from evaluated

`TQuote`

`StdDev`

* double* - Standard Deviation of price

`Mean`

* double* - Mean value of price

`ZScore`

* double* - Z-Score of current price (number of standard deviations from mean)

`StdDevSma`

* double* - Moving average (SMA) of

`StdDev`

based on `smaPeriods`

periods, if specified### Utilities

See Utilities and helpers for more information.

## Chaining

This indicator may be generated from any chain-enabled indicator or method.

```
// example
var results = quotes
.Use(CandlePart.HL2)
.GetStdDev(..);
```

Results can be further processed on `StdDev`

with additional chain-enabled indicators.

```
// example
var results = quotes
.GetStdDev(..)
.GetSlope(..);
```