StDevP() | Calculation Functions

Category: Aggregate

Syntax: `StDevP ( field {; field...} )`

Parameters:

fieldAny related field, repeating field, or set of non-repeating fields that represent a collection of numbers. Parameters in curly braces { } are optional.

Data type returned: Number

Description:

Returns the standard deviation of a population represented by the non-blank values represented in the parameter list. Standard deviation is a statistical measurement of how spread out a collection of values is. In a normal distribution, about 68% of the values are within one standard deviation of the mean, and about 95% are within two standard deviations of the mean.

The difference between the StDevP() and StDev() functions is that StDev() divides the sum of the squares by n-1 instead of by n.

StDevP() can also be calculated as the square root of the VarianceP() of a set of numbers.

Examples:

There are several ways you can manually calculate the standard deviation of a population. One is to take the square root of the sum of the squares of each values distance from the mean, divided by the number of values.

For instance, given the set of numbers 8, 10, and 12, the mean of this set is 10. The distances of each value from the mean are therefore -2, 0, and 2. The squares of these are 4, 0, and 4. The sum of the squares is 8. The standard deviation of the population is Sqrt (8/3), which is 1.633.