(PECL stats >= 1.0.0)
stats_standard_deviation — Returns the standard deviation
stats_standard_deviation ( array $a [, bool $sample = false ] ) : float
Returns the standard deviation of the values in a.
a
The array of data to find the standard deviation for. Note that all values of the array will be cast to float.
sample
Indicates if a represents a sample of the population; defaults to false.
Returns the standard deviation on success; false on failure.
Raises an E_WARNING when there are fewer than 2 values in a.
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https://www.php.net/manual/en/function.stats-standard-deviation.php