Why it is so Important to Know the Monster “Variance”? — part-2Amrendra Roy
Variance occupies the central role in the six-sigma methodology. Any process whether from manufacturing or service industry has many inputs and the variance from each input gets add up in the final product.
Hence variance has an additive property as shown below
Note: you can add two variances but not the standard deviations
Consequence of the variance addition and six sigma
Say if a product/services which is the output of some process, which in turn have many inputs. Then the variance from the input () and from the process () adds up to give the final variance () in the product/services.
DMAIC methodology of 6Sigma try to identify the inputs that contributes maximum towards the variance in the final product and once identified, its effect is studied in detail to minimize the variance from the input. This is done by reducing the variance in the input itself.
Example: if the quality of a input material used to manufacture a product is found to be critical, then steps would be taken to reduce the fluctuation of the quality of that input material from batch to batch either by requesting/threatening the vendor or by performing the rework of the input material at your end.
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