A Black Belt who is evaluating the relationships among three input variables should use which...

The correct answer is C. Multiple linear regression . In the CSSBB Analyze phase, the topic “Measuring and Modeling Relationships” includes regression , correlation coefficient , and multivariate tools . The CSSBB source explicitly states that both simple linear regression and multiple linear regression are discussed in this section. Multiple linear regression is the appropriate tool when a practitioner wants to model or evaluate the relationship between a response and more than one input variable .

The wording “among three input variables” indicates a need to examine how multiple predictors relate within a statistical model. That is exactly the purpose of multiple linear regression in Six Sigma analysis. In contrast, quality function deployment is used for translating customer requirements into design or process characteristics, control charts are for monitoring process stability over time, and a goodness-of-fit test assesses whether data follow a specified distribution. None of those tools is intended for modeling the combined effect of several input variables. Therefore, for a Black Belt evaluating relationships involving three inputs, the proper analytical choice is multiple linear regression , which supports prediction, significance testing, and understanding variable relationships during root-cause analysis.