NARROWING THE SCOPE

The highly structured six sigma methodology includes techniques for funneling and reducing the number of inputs.

Six Sigma is used to identify input variables that are causing the most deviation from target or variation around the target.

Ys are critical to the satisfaction or CTQs critical to quality for our customer

When we want to solve a problem, we can't just keep tackling everything, we have to find out the critical reasons or the influencers, so we follow the six sigma methodology.
It's like a funnel, we start the problem with big Y and so many Xs, Step by step through the measure face.
First, we brainstorm, we map the process, we draw the side book to collect the possible Xs, then use prioritization metrics to narrow the Xs and we collect data for these Xs.
Based on the collected data, using statistics and hypotheses testing, regression, data analysis, and process analysis, we discover the critical Xs, the real vital feu which affects the big Y which is our customer's problem.
Then we set solutions for those problems.
This is a simple summary of Six Sigma DMAIC Methodology.
How we can find the red Xs that affect the Y?
When we control these Xs, we control the Y, When we control the input, we can control the output which affects our customer.