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We illustrate how a Six Sigma project team can apply recursive partitioning to a historical data set to narrow down a list of potential experimental factors and then construct an experimental design using information from the partition analysis. The paper illustrates the value of analyzing historical manufacturing data to inform the choice of factors and levels for statistically designed experiments.

This study investigated the effects of various levels of secondary school calculus experience on performance in first-year college calculus, with focus on student performance on conceptual and procedural exam items. Analysis of covariance, with mathematics SAT score as a covariate, was employed to explore differences among four groups of students. Students who had a year of secondary school calculus, advanced placement or otherwise, differed significantly in performance from students who had either no calculus or a brief introduction to calculus prior to college. A brief secondary school introduction to calculus, in comparison with no secondary school calculus, provided an initial advantage in the college course. This slight advantage reappeared on the final exam and on the procedural subscale of the final exam. Students who had studied a full year of secondary school calculus performed significantly better than other groups throughout the first-semester course. The advantage was revealed more strongly in procedural than in conceptual items. There were no significant differences among the four groups of students on outcome measures in the second-semester course. Students with more secondary school calculus background were more likely to continue into the second semester of college calculus.

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SUMMARYThe Chemoprevention for Barrett's Esophagus Trial (CBET) was a phase IIb, multicenter, randomized, placebo-controlled trial of celecoxib in patients with Barrett's esophagus. The overall outcome of the study was that there were no significant differences in primary, secondary, or tertiary outcomes. The purpose of the current study is to focus on results related to the method of measuring lesion size called quantitative endoscopy (QE). The design includes a review of a total number of studies and then restricts analyses to the four clinics that enrolled more than four patients each for whom a baseline and 1-year QE study was performed, comparing intra-and inter-patient and clinic differences in Barrett's esophagus. Measurements include the number of total QEs and adverse events, changes in areas from baseline to 1 year and other intervals, classification of Barrett's lesion type with respect to patients, clinics, and treatment. A total of 309 QE studies were completed with no adverse events. Differences in surface area measurements over time for a particular patient are smaller than the differences for randomly selected patients. The complexity mix (as defined by the mix of circumferential, tongues, and islands) of the Barrett's lesions varied with different clinics. In conclusion, QE is an efficient, safe, and accurate way to measure the area of Barrett's lesions variation between different clinical sites may be attributable to a subtle type of selection bias at the individual clinics rather than to regional differences.