The optimization procedure picks several starting points from which to begin searching for the optimal variable settings. There are two types of solutions for the search:

·    Local solution: For each starting point, there is a local solution. These solutions are the "best" combination of variable settings found beginning from a particular starting point.

·    Global solution: There is only one global solution, which is the best of all the local solutions. The global solution is the "best" combination of variable settings for achieving the desired responses.

By default, Minitab only displays the global solution.

Minitab calculates the individual desirability for each predicted response. The individual desirability values are then combined into the composite desirability. These desirability values can help you understand how close the predicted responses are to your target requirements. Desirability is measured on a 0 to 1 scale.

Individual desirability: The closer the predicted responses are to your target requirements, the closer the desirability will be to 1. The individual desirability for each response is displayed on the Optimization Plot.

Composite desirability: The composite desirability combines the individual desirabilities into an overall value, and reflects the relative importance of the responses. The higher the desirability the closer it will be to 1.

By default, Minitab places equal importance on the responses and assigns each an importance value of one. You can change the importance to allow some responses to have more influence on the composite desirability than other responses.

·    If you want more emphasis on a response, increase its importance relative to the other responses.

·    If you want less emphasis on a response, decrease its importance relative to the other responses.  

For the tire manufacturing process, to create a product that meets requirements of both quality characteristics, you would set the variables as follows:

·    set temperature at 466.496

·    set curing time at 37.3949

·    set density at 9.31821

The composite desirability of 1.00000 is a perfect score and indicates that both responses achieved their ideal settings.