Glossary Terms Archive

Curvature in DOE: What It Means in Six Sigma and How to Test for It

In Six Sigma’s Design of Experiments, curvature describes a condition where the relationship between a process input (X) and a process output (Y) is not linear. In a two-level factorial design, the model assumes a straight-line relationship between each X and Y....

Cpk Explained: Formula, Benchmarks, and How to Improve It

Your process has been running for weeks. The output looks reasonable. But a customer audit is coming, and they want to see your Cpk. Do you know what it is? More importantly, do you know what it means? Cpk — the Process Capability Index — is one of the most commonly...

Correlation Coefficient

A correlation coefficient is a statistical measure that quantifies the degree of correlation between two variables. It provides insights into the strength and direction of the relationship between variables. In many practical scenarios, we encounter data on two or...

Control Plan Explained: Types, Columns, and the PFMEA Link

A control plan is a living document, not a one-time form. It lists exactly how a team monitors and controls each critical process step. The Automotive Industry Action Group, or AIAG, defines the standard format most manufacturers use. Every entry in a good control...

Control Limits Explained: UCL, LCL, and the 3-Sigma Rule

Control limits mark the boundary between normal process variation and a real problem. Every control chart uses two limits. These are the upper control limit (UCL) and the lower control limit (LCL). Statistician Walter Shewhart set this standard in 1924. He fixed...