A Systematic Approach to Planning for a Designed Industrial

Unfortunately the concept of interactions is not self

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Unformatted text preview: ately, the concept of interactions is not self-explanatory-even among intelligent, mathematically inclined people in the sciences. Hence, as part of the package of guide sheets, it is helpful to include a tutorial. The graphical portion of the tutorial is presented in Figure 6. An additional, expository description of interactions is sometimes included, but it is not shown here. The interactions table explicitly recognizes only pairwise interactions of linear terms. It provides an opportunity for the experimenters to capture knowledge or speculation that certain pairwise interactions may be present and others are unlikely to be present. This input is helpful when the experiment is later designed-to choose resolution, or more generally to choose which effects should or should not be confounded. Higher order effects may also be important but are not captured in the guide sheets. The interaction sheet for the CNC-machining example is shown in Table 6. A helpful way to use this matrix is to avoid discussing every possible pairwise interaction one at a time but instead use the process of elimination or inclusion; that is. if interactions are generally imTECHNOMETRICS, FEBRUARY 1993, VOL. 35, NO. 1 C. MONTGOMERY Factors Strategy (e.g., randomization, blocking, etc. ) Measure viscosity start and end Make runs below 80°F. Anticipated at Block or randomize on machine spindle Do not move heavy objects in CNC machine shop effects None to slight Slight, unless very hot weather Spindle-to-spindle variation could be large Severe vibration can introduce variation within an impeller portant, a question can be posed: “Are there any interactions that are arguably not present‘?” If main effects dominate interactions, a question can be posed: “Are there any interactions that must be estimated clear of main effects?” Alternatively, a secret-ballot vote on potentially important interactions can be held among experimenters and other knowledgeable investigators, with each receiving, say. 1...
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