A Systematic Approach to Planning for a Designed Industrial

The relationship of a response variable to the

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Unformatted text preview: tion. The relationship of a response variable to the objective may be direct. An objective may be defined in terms of a response variable-for example, “to quantify the effect that thermal cycle B has on tensile strength measured on customer qualifying tester X.” In the case of CNC-machining, a response variable is blade profile (see Fig. 4). This is related to the objective through two measurement-performance indicators-mean absolute difference of blade profile and the target, and standard deviation of the difference. Sometimes a response variable may be a SUTrogate for the true response of interest. This is often the case in destructive testing, in which a standard stress-to-fracture test, for example, represents performance under conditions of use. Another example is yield rate or failure rate, which are inferior responses that often represent where a specification falls relative to a distribution of continuous-scale values (the collection of which provides superior information). As discussed previously, the relationship of a response variable to the objective may be through performance measures that involve a comparison of the response to a target or desirable outcome. 4. CONTROL VARIABLES As with response variables, most investigators can easily generate a list of candidate control variables. Control variables can be attribute or continuous. They can be narrowly defined, such as “percent of copper, by weight,” or broadly defined, such as “comparably equipped pc: Apple or IBM.” In either case, control variables should be explicitly defined. When discussing potential control variables with experimenters, it may be helpful to anticipate that held-constant factors and nuisance factors must also be identified. Figure 5 is a Venn diagram that can be used to help select and prioritize candidate factors. It illustrates different categories of factors that affect response variables, based on three key characteristics-magnitude of influence on response variables, degree of controllability,...
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