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Special cause/ Assignable Cause (Quality)

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nazrulq
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Special cause/ Assignable Cause (Quality)

Postby nazrulq Mon Jul 24, 2017 5:29 am

When Data point or points are out side any control limit even on specification limit range. That is called a Special cause.
In Rita's book, assignable cause shows data point is on specification limit. How about if 3 data points are located above or below control limit (+/-3 sigma)/. That is also explained the process is out of control and to be inspected as per PMBOK.
This is to mention Specification limit is beyond control limit assigned by the customer.

Can Manish explains elaborately!
manishpn
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Re: Special cause/ Assignable Cause (Quality)

Postby manishpn Mon Jul 24, 2017 12:20 pm

nazrulq wrote:When Data point or points are out side any control limit even on specification limit range. That is called a Special cause.

Special/assignable cause is when the process is out of control and an action has to be taken to bring it back in control
process can be out of control in case there is a data point which falls outside the limits or consecutive 7 data points are on one side of mean. Its is as simple as that.


In Rita's book, assignable cause shows data point is on specification limit.

Yes thats ok , recall definition of control and specification limit, control limit is performing organization standard which is usually stricter than specification limit, so if any data point is outside control limit the process is out of control.
How about if 3 data points are located above or below control limit (+/-3 sigma)/.

Even if one data point is outside control limit its special cause that need action.

That is also explained the process is out of control and to be inspected as per PMBOK.
This is to mention Specification limit is beyond control limit assigned by the customer.
Not necessarily but usually specification limit is beyond control limit, however sometimes customer may have stringent requirements and your organization operates in less stringent environment , then in that case the specification limit may be below control limit,

Can Manish explains elaborately!
Br,
Manish P
PMP, PMI - ACP, SAFe Agilist
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