Glossary Terms Archive

Contour Plot: Definition, How to Read One, and the Overlay Trick Most Miss

A contour plot is a two-dimensional graph that shows how two input variables (X1 and X2) affect one output (Y), using curved lines to connect every combination of inputs that produces the same output value, similar to elevation lines on a topographic map. It is the...

Confounding

Confounding is a crucial concept in research. It describes a situation where a third variable influences both the independent and dependent variables. This creates a spurious association. It makes it seem like the independent variable is causing the dependent...

Confidence Interval in Six Sigma: A Plain-Language Guide

You measure a sample of parts and find the average diameter is 10.2mm. But how reliable is that number? Does it describe the whole process, or just the 30 parts you happened to measure? This is exactly the problem a confidence interval solves. A confidence interval...

Coefficient of Determination (R²): What It Really Tells You

The coefficient of determination, written R² and read “R-squared,” is the proportion of variation in an output (Y) that a regression model explains using its input variable(s), expressed as a value between 0 and 1, or 0% to 100%. An R² of 0.75 means the...

Chi-Square Test: Definition, Examples, and How to Use It in Six Sigma

A chi-square test is a statistical hypothesis test used to determine whether observed counts in categorical data differ significantly from what would be expected by chance. It comes in two forms that get confused constantly: a goodness of fit test, which checks...