michiel / nelsonrules-js

Statistical process control rules for embedding in JavaScript capable environments

Nelson Rules - JavaScript

The rules

These are taken from Wikipedia

Nelson Rule 01

• One point is more than 3 standard deviations from the mean.
• At least one sample is grossly out of control.

Nelson Rule 02

• Nine (or more) points in a row are on the same side of the mean.
• Some prolonged bias exists

Nelson Rule 03

• Six (or more) points in a row are continually increasing (or decreasing).
• A trend exists.

Nelson Rule 04

• Fourteen (or more) points in a row alternate in direction, increasing then decreasing.
• This much oscillation is beyond noise.

Nelson Rule 05

• Two (or three) out of three points in a row are more than 2 standard deviations from the mean in the same direction.
• There is a medium tendency for samples to be mediumly out of control.

Nelson Rule 06

• Four (or five) out of five points in a row are more than 1 standard deviation from the mean in the same direction.
• There is a strong tendency for samples to be slightly out of control.

Nelson Rule 07

• Fifteen points in a row are all within 1 standard deviation of the mean on either side of the mean.
• With 1 standard deviation, greater variation would be expected.

Nelson Rule 07

• Eight points in a row exist, but none within 1 standard deviation of the mean, and the points are in both directions from the mean.
• Jumping from above to below whilst missing the first standard deviation band is rarely random.

Nelson Rule 08

• Eight points in a row exist, but none within 1 standard deviation of the mean, and the points are in both directions from the mean.
• Jumping from above to below whilst missing the first standard deviation band is rarely random.