In the factorial design main-effects plot shown, which factor setting gives the lower response?

The correct answer is D, Factor B low, because the main-effects plot indicates that the response is lowest at the low setting of factor B. In a main-effects plot, the average response is plotted at each level of each factor, and the team compares the height of those plotted means to determine which settings increase or decrease the outcome. The factor level associated with the lowest plotted point gives the lowest average response. In Six Sigma Analyze and Improve work, this is a fundamental DOE interpretation skill. Black Belts use main-effects plots to identify which factor settings move the response in the desired direction and to determine promising operating conditions for further study or optimization. The steeper the line, the stronger the main effect of that factor on the response. This question focuses only on identifying the lowest response setting, and from the plot that point occurs at factor B low. Therefore, the correct answer is D, because the low level of factor B corresponds to the minimum response among the settings shown.

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