Special cause & Common cause

Submitted by san on Mon, 06/10/2013 - 07:28

Which one is easy to predict between special cause and common cause in control chart

which one is easy to handle between special cause and common cause in control chart

 

Please provide the explanation.

Thanks

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PMP / CAPM exam Question bank
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cnppmp

Mon, 06/10/2013 - 10:04

 

Common Cause:

In a constant-cause system the variations in a measured variable are considered due to chance and to remain in the system unless the process is itself altered. Such causes are referred to as
common causes.

Examples of Common Causes:
• Variations in environmental variables such as temperature and humidity
• Variations among machines
• Variations among worker’s skills
• Variations in raw materials

Overreacting to common-cause variation usually leads to “tampering” with a process
that may already be in control.This in turn leads to increased variation in process results
****************************************************************************************************************

Special Cause:

The variation observed is considered to be the effect of many, individually small, unobserved influences.

Special causes are individually important and affect process results only some of the time.
They arise because of special circumstances

On the other hand, failing to detect and deal with special causes means a lost opportunity
to eliminate variation in the process

Examples of Special Causes:
• Temporary change to a new supplier
• Temporary worker not properly trained
• Intermittent power failure
• Ice storm
• Bird in the toothpaste vat

 

A process is considered to be in control (or stable) if only common causes are operable
and no special causes are influencing the variability of process results

 

Regards

CN Patil

san

Mon, 06/10/2013 - 12:52

Thanks for your explanation for the individual causes. Can you answer the following two questions

Which one is easy to predict between special cause and common cause in control chart

Is special cause correct?

which one is easy to handle between special cause and common cause in control chart

Not sure on handling the causes..

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cnppmp

Mon, 06/10/2013 - 15:43

Which one is easy to predict between special cause and common cause in control chart

Is special cause correct?

Ans)

Special cause is unpredictable / but can be fixed ultimately working on the root cause.

Common cause is predicatable but needs to be accepted since you know the outcome. For example if you machine with a problem, here the outcome is known on the end product produced out of that machine that you would get some type defect or deviation..this known (predictable ) but unless you replace the machine you would tend to get such product out of that machine which is inevitable

 

which one is easy to handle between special cause and common cause in control chart

Not sure on handling the causes..

Ans) The special cause pertains to control chart, which give you picture of process in conntrol and out of control. I would think Special cause is much easy to handle than common cause.

 

Regards

CN Patil

sanskrit

Tue, 06/11/2013 - 12:31

 Great explanation , I wish i had this information/explanation  for  Special cause & Common cause when I was preparing for PMP, Aftre reading this explanation  there is no way you will forget the difference between Special cause & Common cause, Also will get alll the Special cause & Common cause questions right !

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cnppmp

Tue, 06/11/2013 - 13:14

Thanks Sanskrit...

regards

CN Patil