A (n) ________________ has occurred when two inputs have a greater impact on a change in the output than either of the inputs has by itself.

In Design of Experiments (DOE), an interaction occurs when the effect of one input variable (factor) on the output response depends on the level of another input variable. This means the combined effect of the two inputs is greater (or different) than the sum of their individual main effects. Identifying interactions is a primary reason Lean Six Sigma practitioners use factorial designs rather than one-factor-at-a-time (OFAT) experimentation.

A. Dependency: This refers to general statistical dependence between variables but is not the specific DOE terminology for combined factor effects on an output.

B. Bimodal reaction: This refers to a statistical distribution with two distinct peaks, not the combined effect of input factors.

D. Amplified effect: This is a generic descriptive phrase, not a recognized statistical term in DOE for this specific phenomenon.

1. Montgomery, D. C. (2017). Design and Analysis of Experiments (9th ed.). John Wiley & Sons. (Section 5.1 Introduction to Factorial Designs, p. 184).

2. NIST/SEMATECH e-Handbook of Statistical Methods, Section 5.3.3.3. "How do you interpret interaction effects?".