Donald  J Wheeler, provides a concise summary of the key elements of Process variation in his book “Understanding Variation“. He has also included a summary of the contents presented as “Lessons” along with the Appendix

Below are some of the Key concepts of importance

DATA PRESENTATION
– Data should always be presented in such a way that preserves the evidence in the data, for all the predictions that may be made from the data

– whenever an average range or histogram is used to summarize data, the summary should not mislead the user into taking action, that the user would not take if the same is presented in a time series.

DATA INTERPRETATION

1. No data has meaning apart from their context

2. No matter how the data is presented, one should consistently use the same analysis methods for interpreting data

3. Flawed Assumptions & Flawed presuppositions, can result in flawed interpretations.

when people are pressurized to meet a target value, there are three ways they can proceed
1) They can work to improve the system
2) They can distort the system
3) or they can distort the data

PROCESS VARIATION

Predictions and specifications should not be taken as targets.A predictable process displays routine variation. An Unpredictable process displays both routine and exceptional variation. The Specification approach and the average value approach attempts to attach a meaning to each and every value. The Process behavior chart, concentrates upon the behavior of the underlying process.

Two mistakes in analyzing the data
1. Interpreting noise ( routine variation) as if it were a signal
2. Failing to detect a signal when it is present

Every potential data analysis begins by separating the potential signal from probable noise. While every data set contains noise, some data set may contain signal, therefore before you can detect a signal within every data-set, you must first filter out the noise

IN CONCLUSION

Before you can improve the system, you must listen to the voice of the system (voice of the process) then you must understand how the inputs affect the output of the system, Finally you must be able to change the inputs (and possibly the system) in order to achieve the desired results.

The Best Analysis is the simplest analysis, which provides the needed insight