The Planning Phase is Crucial

• A DOE effort will fail if not properly planned. The team or individual responsible for the experiment needs to take the time to think through the entire activity.

• Without good planning, the DOE might yield poor results or, even worse, lead to misleading conclusions.

Steps for Designing an Experiment

• Design & Communicate the Objective

• Define the Process

• Select a Response and Measurement System

• Ensure that the Measurement System is Adequate

• Select Factors to be Studied

• Select the Experimental Design

• Set Factor Levels

• Final Design Considerations

Design & Communicate the Objective

• The objective will generally be one of three forms:

  • The “Biggest” (maximize the response)

  • The “Smallest” (minimize the response)

  • The “Closest-to-Target” (hit a target)

Define the Process

• Define the boundaries of the process to be experimented upon.

• This could be just internal processes or it could include the full extended process in which the processes of suppliers and/or customers are studied along with internal processes.

Select a Response and Measurement System

• Responses are the outputs, or the dependent variables, of the process. In analyzing a designed experiment, you can use as many responses as you are willing to measure.

• A good measurement system is one that is accurate, repeatable, reproducible, stable, and linear.

• Taking good samples is a critical aspect of the measurement system. The samples from each experimental run must be representative of the response during that run.

Ensure that the Measurement System is Adequate

• Make sure the measurement system has been calibrated.

• If the measurement system is not repeatable and reproducible, the results of the designed experiment will not be valid.

Select Factors to be Studied

• Factors are the independent variables that will affect the response; select those factors that should have the greatest impact on the response.

• Ensure that it is practical, feasible, and cost effective to select a factor to be studied and to change its level.

Select the Experimental Design

• The type of design is highly dependent on the number of factors to be studied.

• Screening experiments are usually the best design choice early in an experimental sequence when many factors are to be explored.

Set Factor Levels

• Be bold and set the levels at the edges of the operating window for the process for screening experiments.

Final Design Considerations

• Final considerations include:

  • Selecting the experimental matrix to use;

  • Deciding how to estimate the experimental error; and

  • Planning the experiment out so that any external sources of variation are minimized.