# periodToDateStDev

The periodToDateStDev function calculates the standard deviation of the set of numbers in the specified measure for a given time granularity (for instance, a quarter) up to a point in time, based on a sample and relative to that period.

## Syntax

`periodToDateStDev(`

measure,

dateTime,

period,

endDate (optional))

## Arguments

measure

The argument must be a field. Null values are omitted from the results. Literal values don't work.

dateTime

The Date dimension over which you're computing PeriodToDate aggregations.

period

(Optional) The time period across which you're computing the computation. Granularity of YEAR means YearToDate computation, Quarter means QuarterToDate, and so on. Valid granularities include YEAR, QUARTER, MONTH, WEEK, DAY, HOUR, MINUTE, and SECONDS.

endDate

(Optional) The date dimension that you're ending computing periodToDate aggregations. It defaults to now() if omitted.

## Example

The following example calculates the week-to-date minimum fare amount per payment type, for the week of 06-30-21. For simplicity in the example, we filtered out only a single payment. 06-30-21 is Wednesday. Insights begins the week on Sundays. In our example, that is 06-27-21.

`periodToDateStDev(fare_amount, pickUpDatetime, WEEK, parseDate("06-30-2021", "MM-dd-yyyy")`