Comparing Reliabilities of the Strength of Two Container Designs: A Case Study

10.6339/JDS.2003.01(2).113

Esteban Walker；Frank Guess

Bursting strength ； early mortality ； lack of fit ； mixture ； Weibull

Journal of Data Science

1卷2期（2003 / 05 / 01）

185 - 197

英文

Two designs for PET (polyethylene terephthalate) beverage bottles were compared. These bottles are used for carbonated beverages; and thus, a very critical property is their burst strength. The burst strengths of bottles from each design across 24 cavities were measured. Standard nonparametric methods suggested a highly significant difference in the reliability of the two designs. Using simple graphical techniques, it was found that the reliability data of the new design appeared to be a mixture of distributions caused by the presence of ”arly mortality,” due possibly to different failure modes. Even though they were clearly different, neither design was uniformly more reliable than the other. Standard parametric methods showed inadequate fit due to the bimodality of the strength data of the new design. The paper stresses (1) the need of operational clear definitions for ”reliability,” (2) the need of graphical exploratory analysis to discover anomalies in the data, and (3) the value of nonparametric methods, and (4) the problems of using parametric techniques when the assumptions are violated. To justify work on improvement of the new design, the potential effect of the removal of the early mortality on the new design was analyzed.