Six Sigma Green Belt Certification Practice Exam

Which option represents the main characteristic indicating a significant interaction on an interaction plot?

1. Steep line

2. Parallel lines

3. Lines consistently far apart

4. Non-parallel lines

The correct answer is: Non-parallel lines

The main characteristic indicating a significant interaction on an interaction plot is when the lines are non-parallel. When the lines representing different groups in the plot cross or diverge, it signifies that the effect of one independent variable on the dependent variable changes depending on the level of another independent variable. This interaction effect implies that the relationship between one factor and the outcome is influenced by the presence of another factor, which is a clear indicator of interaction. In contrast, parallel lines would indicate no interaction, meaning each factor independently affects the outcome without influencing each other. Steep lines, while they may suggest a strong effect of one variable, do not inherently signify interaction on their own. Lines consistently far apart could indicate different levels of effect but do not reveal the nature of interaction—whether it is significant or not. Thus, non-parallel lines are the definitive visual cue for identifying significant interactions in an interaction plot.