Example of a response trace plot
main topic    interpreting results     session command     see also     

In the Example of a simplex centroid design, you created a design to study how the proportions of three ingredients (neroli oil, rose oil, and tangerine oil) in an herbal blend household deodorizer affect the acceptance of the product based on scent. Next, you analyzed the response (Acceptance) in the Example of analyzing a simplex centroid design. Now, to help you visualize the component effects, you display a response trace plot.

1    Open the worksheet DEODORIZ2.MTW.

2    Choose Stat > DOE > Mixture > Response Trace Plot.

3    Click OK.

Graph window output

Interpreting the results

The trace plot shows how each component effects the response relative to the reference blend. The reference blend is shown in the legend of the plot. In this example, the reference blend is the centroid of the design vertices; each component represents 0.33 of the total. This trace plot provides the following information about the component effects. Starting at the location corresponding to the reference blend:

·    As the proportion of neroli oil in the mixture

-    increases (and the other mixture components decrease), the acceptance rating of the deodorizer decreases

-    decreases (and the other mixture components increase), the acceptance rating of the deodorizer decreases

The proportion of neroli oil in the reference blend is near optimal.

·    As the proportion of rose oil in the mixture

-    increases (and the other mixture components decrease), the acceptance rating of the deodorizer decreases slightly

-    decreases (and the other mixture components increase), the acceptance rating of the deodorizer increases

A decrease in the proportion of rose oil relative to the reference blend may improve the acceptance rating.

·    As the proportion of tangerine oil in the mixture

-    increases (and the other mixture components decrease), the acceptance rating of the deodorizer increases slightly

-    decreases (and the other mixture components decrease), the acceptance rating of the deodorizer decreases

An increase in the proportion of tangerine oil relative to the reference blend may improve the acceptance rating.

Keep the following in mind when you are interpreting a response trace plot:

·    All components are interpreted relative to the reference blend.

·    Components with the greatest effect on the response will have the steepest response traces.

·    Components with larger ranges (upper bound - lower bound) will have longer response traces; components with smaller ranges will have shorter response traces.

·    The total effect of a component depends on both the range of the component and the steepness of its response trace. The total effect is defined as the difference in the response between the effect direction point at which the component is at its upper bound and the effect direction point at which the component is at its lower bound.

·    Components with approximately horizontal response traces, with respect to the reference blend, have virtually no effect on the response.

·    Components with similar response traces will have similar effects on the response.