Calculating out-of-bounds values using standard deviation

stddev.sql

with nums as (
	select * from (values (18), (3), (3), (2), (4), (2), (5), (3), (12), (0.00003), (4), (2)) as n (x)
), a as (
	select
	stddev(nums.x) as sdev, 
	abs(avg(nums.x)) as aavg, 
	numrange(
		(abs(avg(nums.x) - stddev(nums.x))),
		(abs(avg(nums.x) + stddev(nums.x)))
	) as bounds
	from nums
)
select nums.x, a.aavg, a.sdev, a.bounds, a.bounds @> nums.x::numeric from nums, a;