Search

A procedure is proposed for screening applications in quality control that eliminates overselection (namely, the condition where the proportion of accepted screened items is greater than the proportion of conforming [...]

William J. Kolarik WCB/McGraw-Hill, 641 pp., ISBN 0-07-036309-9 With growing global competition, quality management is becoming increasingly important to the leadership and management of all organizations. There are widely accepted [...]

There are different approaches for studying linear models (and multivariate statistical analysis in general); for example, decision analytic approach, algebraic approach, and geometric approach. Quite a few books on linear [...]

Accelerated Life Testing (ALT) is used to provide timely estimates of a product's lifetime distribution. Step-Stress ALT (SSALT) is one of the most widely adopted stress loadings and the optimum design of a SSALT plan has been extensively studied. However, few research efforts have been devoted to establishing the theoretical rationale for using SSALT in lieu of other types of stress loadings. This article proves the existence of statistically equivalent SSALT plans that can provide equally precise estimates to those derived from any continuous stress loading for the log-location-scale lifetime distributions with Type-I censoring. That is, for any optimization criterion based on the Fisher information matrix, SSALT is identical in comparison to other continuous stress loadings. The Weibull and lognormal distributions are introduced as special cases. For these two distributions, the relationship among statistical equivalencies is investigated and it is shown that two equivalent ALT plans must be equivalent in terms of the strongest version of equivalency for many objective functions. A numerical example for a ramp-stress ALT, using data from an existing study on miniature lamps, is used to illustrate equivalent SSALT plans. Results show that SSALT is not only equivalent to the existing ramp-stress test plans but also more cost-effective in terms of the total test cost. [ABSTRACT FROM AUTHOR]

A procedure is proposed for screening applications in quality control that eliminates overselection (namely, the condition where the proportion of accepted screened items is greater than the proportion of conforming items in the original population) and controls for individual unit misclassification error (IME), namely, the probability of an accepted/selected item being below specification. Screening involves selecting items whose performance is within specifications based on observing one or more correlated screening variables in lieu of observing the performance variable directly. Overselection and an uncontrollably high IME can occur when (1) there is a high correlation between the performance and screening variables and (2) the proportion of conforming items among accepted items (or its complement, average outgoing quality (AOQ)), is prespecified as in, for example, Owen et al. (1975). We instead propose a procedure that prespecifies a maximum tolerable IME (emaxa) for accepted items, which eliminates overselection and assures that the IME of each outgoing item as well as the AOQ are both equal to or less than emaxa. The quality of each individual item as well as AOQ is thereby explicitly controlled. Only the use of standard normal tables is required to implement our proposed procedure. [ABSTRACT FROM AUTHOR]

When inspection on the performance variable of interest is destructive or costly, it is attractive to use other variables which are correlated with the performance variable and which are inexpensive to inspect as the screening variables. The idea of using a single correlated variable in a complete screening procedure has drawn much attention recently. In this paper, we extend a previously defined economic model for a screening procedure using more than one correlated variable. The screening specifications are based on a linear combination of the correlated variables, and if an item fails to conform to the screening specifications, it is rejected and excluded from shipment. The screening specifications are determined so that the total cost, the sum of three components, is minimized. [ABSTRACT FROM AUTHOR]

The process distribution of a manufacturing process which reflects past experience with the quality levels of outgoing lots is an indispensible input of the Bayesian quality audit systems. A distance-method estimator for the process distribution is developed and shown to be superior to the commonly used method-of-moments estimator. En a continuous manufacturing process, the process distribution needs to be updated after each new lot is inspected. Several updating procedures including the posterior distribution, the exponential smoothing method, the moving window method and the all periods method are proposed and compared by a simulation study. [ABSTRACT FROM AUTHOR]