Question

Distinguish between chance cause and assignable cause

Answer 1

The difference between the Chance cause and Assignable cause is given as follows:

Chance cause:

• A form of variation noticed in a quantitative feature, process, or measurement that is attributable to a random change in any aspect involved until the output is received is known as the chance cause.
• It's also considered a "natural cause", and it doesn't produce a lot of variance in the output.
• Mild vibration of a production machine, for example, because it is no longer in operation.

Assignable cause:

• The assignable cause is a sort of variation that has affected the result owing to a deviation due to a particular reason that can be easily found through troubleshooting.
• It's also known as a "special cause" and it can produce a lot of variation in an output.
• For example, due to faulty raw materials, the entire batch of tablets was determined to be defective.

Answer 2

The differences between a chance cause and assignable cause are,

Chance cause:

• 'Chance causes of variability' are the common, inherent and naturally occurring variability of a process. It can be simply termed as the 'background noice' of the process.
• The chance causes are an inherent part of the process. They are usually accidental and does not purposefully cause the occurence of any event. The incidents that happens by chance.
• The usual process performance is disturbed by the variations created from assignable or special causes. It is said to be in statistical control and hence cannot be economically removed by the operator.      

Assignable cause:

• "An assignable cause can be defined as a source of variation that is intermittent, not predictable". It is mentioned as a special cause.  
• When indicating in a control chart, the assignable causes are marked by points that are beyond the control limits and are not in a random pattern.
• It indicates a linear trend of increasing or decreasing slope of 7 consecutive points. It is recurring as a cycle in a repeating fashion. It elongates as 8 points outside the average or centre line.