What are chance and assignable causes of variability What pa

What are chance and assignable causes of variability? What part do they play in the operation and interpretation of a Stewhart control chart?

Solution

Chance Causes Assignable Causes (i) Consist of many individual causes. Consists of one or just a few individual causes. (ii) Any one chance causes results in only a minute amount of variation. (However, many of the chance causes act simultaneously so that the total amount of chance variation is substantial). Any one assignable cause can result in a large amount of variation. (lit) Some typical chance causes of variation are : (a) Slight variations in raw material (though within the specifications) (6) Slight vibration of machine (c) Lack of human perfection in reading instruments and setting controls. Some typical assignable causes of variation are : Batch of defective raw material Faulty set up Untrained operator (jy) As a practical matter, chance variation cannot economically be eliminated from a process. The presence of assignable variation can be detected and action to eliminate the causes is usually justified.