WORLD CLASS QUALITY, by Keki R. Bhote, page 53:
……Shainin the MASTER PROBLEM SOLVER. Shainin a portly man. ……. is truly worth his weight in gold ……. for his tremendous contribution to SPC and the design of experiments, DOE’s.

The power of the Shainin techniques is captured in his statement:

“LISTEN TO THE PARTS, THEY’RE SMARTER THAN THE ENGINEERS”

What he means is, don’t guess, also known as engineering judgement, which variables are important (and thereby excluding hundreds of others), and then
run long, expensive, and often non-productive DOE’s. Instead, use his “listening”
tools to separate THE CRITICAL FEW FROM THE TRIVIAL MANY!

In Shainin parlance, find the “RED X”;.

Tools for solving UNSOLVABLE quality problems are characterized as:

• Robust and simple. Almost embarrassingly so,
• KISS: Keeping It Statistically Simple. No complex formulas, and
• Simple enough so that direct labor can use them, and sometimes even
  the engineers.

Three favorite “listening”, or separation, tools are:

1 – THE PARETO PRINCIPLE: i.e. 80% of the undesirable output “Y” is caused
by 20% of the causes, “X1”.

Hence by analyzing the “Y” defect categories (X’s), clues are obtained about the
to root cause, i.e. X1, the number 1 Pareto defect, and

2 – DEVIATIONS ADD AS THE SQUARE ROOT OF THE SUM OF THE
SQUARES:

• Changing 1.0 to 0, only changes the hypotenuse to 5.0
• But changing 5.0 to 4.0 changes the hypotenuse to 4.1. A 10X difference!!!
• Hence the RED “X” impact is magnified like a sore thumb.

3 – MULTI-VARI ANALYSIS:

• Next we plot 'Y' deviations for defect X1 in, positional, cyclical, and time format, known as a multi-vari analysis. From the plot, shown below, we can get fast clues about the root cause “RED “X”. Is it a positional, cyclical, or a time-to-time dependent deviation? For example: