THE TREATMENT OF RELATED EXPERIMENTAL FACTORS BY SLIDING LEVELS

Two factors are related when one factor's desirable range depends on t he level of another factor. For example, in a chemical reaction, the d esirable reaction-time range shifts downward as temperature increases. This is reflected in the experimental design by choosing levels of on e factor that depend on the level of the other factor. Taguchi refers to this technique as sliding levels and justifies it by rationales of bad region avoidance and interaction elimination. We explore these rat ionales and their implications. In particular, we point out problems w ith Taguchi's analysis strategy which is based on the latter rationale . We propose an alternative analysis method and demonstrate it by rean alyzing three documented experiments; the reanalysis provides new insi ght about their respective processes. Finally, using the bad region av oidance rationale, we discuss alternative experimental designs.