Control chart

[suresi00]

You are using control charts to perform quality control. Which of these situations does not indicate that the process is out of control and an assignable cause needs to be assigned. Assume that the control limits have been set to three sigma.
One of the point is more than the mean + (3*sigma)
Two points together are more than mean +(2*sigma), but less than mean + (3*sigma)
Seven points together are on one side of the mean.
Six points together are on one side of the mean.

I think there is a mistake in the question. Why do we have to give assignable cause when the points are between 2 sigma and three sigma

Source:

https://www.edwel.com/Free-Resources/PM ... -Exam.aspx

[manishpn]

Am not an expert on Sigma
maybe someone else can contribute