Reference · Statistics

stats.stdev

stats.stdev(list, num | null=) -> float

What it does

The sample standard deviation of a list of numbers: the square root of stats.variance, as Python's statistics.stdev. It is the std that stats.describe reports. For the whole population use stats.pstdev.

Examples

print(stats.stdev([1, 2, 3, 4]))print(stats.stdev([1.5, 2.5, 2.5, 2.75, 3.25, 4.75]))

1.29099444873580561.0810874155219827

Edge cases

• At least two numbers are needed: one number is an error, not 0.0.
• A constant list gives 0.0.
• A second argument, a mean already known, is accepted, but the answer is the spread about the data's own mean whatever is given, as in Python before 3.11. Leave it out, or pass null.
• It is the square root of stats.variance exactly.

print(stats.stdev([7, 7, 7]), stats.stdev([1, 2], 1.5), stats.stdev([1, 2], null))print(stats.stdev([1, 2, 3, 4]) == math.sqrt(stats.variance([1, 2, 3, 4])))print(stats.stdev([1, 2, 3, 4]) == stats.describe([1, 2, 3, 4]).std)

0.0 0.7071067811865476 0.7071067811865476truetrue

Errors

Fewer than two numbers is a runtime error, not an error value: an empty list, null or a list of one stops the request. So does an item that is not a number.

print(stats.stdev([5]))

line 1: `stats.stdev` requires at least 2 data points

Chaining

let xs = [2, 4, 4, 4, 5, 5, 7, 9]print(xs | stats.stdev | round(3))let m = stats.mean(xs)let s = stats.stdev(xs)print(xs | filter((x) => x > m + s))

2.138[9]

See also

stats.pstdev, stats.variance, stats.describe, stats.zscore

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