How is Quality Measured?

The word “quality" is used by a lot of people in different contexts. In most companies it is recognized that quality of a service or a product is very important. However, it is very hard to give a perfect definition that discriminates products or services of bad quality from products or services of high quality.

The first to study the ARL of the EWMA was Roberts (1959). Roberts (1959) first introduced the exponentially weighted moving average (EWMA) control scheme. Using simulation to evaluate its properties, he showed that the EWMA is useful for detecting small shifts in the mean of a process Using simulation results, he derived nomograms for the ARL of normally distributed variables.

Numerical results were obtained by Robinson and Ho (1978) they evaluated the ARL of the EWMA control chart using Edge worth expansion.

Crowder (1987) showed that the ARL of the EWMA chart can be written as a so-called Fredholm integral of the second kind. The ARL curve can then be evaluated by approximating the integral numerically.

Lucas and Saccucci (1990) used a Markov-chain approach to evaluate the ARL of the EWMA control chart. They described three enhancements of the EWMA chart that were presented earlier by Lucas and Crosier (1982) for use with the CUSUM chart. These included a so-called FIR feature, which made the control chart more sensitive at startup, a combined Shewhart EWMA chart, which was sensitive in detecting both large and small shifts in µ and robust EWMA, that provided protection against outliers.

Lucas and Saccucci (1990) evaluated the properties of an EWMA control scheme used to monitor the mean of a normally distributed process that may experience shifts away from the target value. A design procedure for EWMA control schemes ...

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... number was determined for exponentiated Weilbull distributions when the consumer’s risk ,test end time and the group are required. The operating characteristic values are obtained at different quality levels.

Aslam et al (2013) proposed the optimal design of skip lot group acceptance to the Weilbull distribution and generalized exponential distribution sampling schemes.in this an article proposed the skip lot sampling plan of type SKSP-2 using a group acceptance sampling for a time truncated experiment as the reference plan, called SKGSP-2 , when the product follows either the generalized exponential distribution or the Weibulll distribution provided tables for industrial use. The proposed plan was found efficient than the existing plan to reach a decision on the lots offered. The scheme can be used for products whose durability has been a generalized distribution.