Six Sigma Quality of NVH refinements of vehicles

Six Sigma quality is a well-known concept in all areas of engineering. How far is it revealed for production passenger cars and commercial vehicles for their Quietness or vibrations within limits ?

Below please find the past data of 3 leading passenger cars in India related to NVH ... defects per 100 vehicles:

In certain areas, the quality was close to 3 sigma levels [for 6-sigma if only 3 defects are allowed per 10 lakh vehicles, 3-sigma indicates 67k defects!]

if course, there must have happened a lot of improvement in this area for recent popular cars.

Still, this is a great challenge to maintain NVH level same in all production vehicles due to various "Noise" and "Error" parameters in the system. But what expert Engineers struggle to find out are the best "Control" factors as shown below ...

Some examples of the above P=diagram as per Taguchi principles applicable to limited Vehicle loads are as follows:

This is just a brief interaction on this challenging topic .... the above Table will expand to each and every critical component & subsystem of the vehicle to live a well-known principle:

" We need to make millions of vehicles quieter and not just a few ones ! "