Source: Red Hat ( Matteo Mortari)
The specification in chapter "10.3.4.4 List functions" for built-in function stddev does not explicit if it's meant to be population or sample standard deviation.
However based on the example provided "stddev( 2, 4, 7, 5 ) = 2.0816659994661" would indicate it is meant to be the standard deviation --which is undefined for a single 1 sample value
In order to be explicit, it is suggested to change the table entry as:
Name(parameters) Parameter Domain Description Example stddev( list )
stddev( n 1 , ..., n n )
list is a list of number. n 1 ... n n are numbers. Returns the
(sample) standard deviation of the list of numbers. If the list is empty,
returns null. If the list contains only one number item, if n is a single number returns null.
stddev( 2, 4, 7, 5 ) =
stddev( [ 47 ] ) = null
stddev( 47 ) = null
stddev( [ ] ) = null
Reported: DMN 1.2b1 — Fri, 18 Jan 2019 15:30 GMT
Updated: Tue, 7 May 2019 14:59 GMT