A unification and some corrections to Markov chain approaches to develop variable ratio sampling scheme control charts

in Statistical Papers (2009)

We provide some unifying definitions, make some corrections to articles by Faraz and Parsian (J Stat Pap 47:569–593, 2006) and Costa (JQual Technol 26:155– 163, 1994; 29:197–204, 1997), and using these ... [more ▼]

We provide some unifying definitions, make some corrections to articles by Faraz and Parsian (J Stat Pap 47:569–593, 2006) and Costa (JQual Technol 26:155– 163, 1994; 29:197–204, 1997), and using these provide more accurate tables of results and comparisons of control charts. We also investigate the impact of an incorrectly specified process shift on signal frequency. [less ▲]

Fuzzy Control Chart A Better Alternative for Shewhart Average Chart

in Quality & Quantity (2007), 41(3), 375-385

This paper through a real illustrative example and a power test shows that designing a fuzzy control chart for process average of a continuous (variable) quality characteristic with a warning line is a ... [more ▼]

This paper through a real illustrative example and a power test shows that designing a fuzzy control chart for process average of a continuous (variable) quality characteristic with a warning line is a better alternative to Shewhart ¯X chart in many respects, like providing better neural view to inspectors, offering different strategic options for company to choose, detecting the desire shifts more quickly, and more sensibility to small shifts without any complexity augmentation to the chart. [less ▲]

Monitoring delivery chains in a supply chain using multivariate control charts

E-print/Working paper (n.d.)

The theory of the delivery chain considers the delivery of goods and services to customers within a specific time interval. Nowadays, organizations are focusing to satisfy their customers’ demands not ... [more ▼]

The theory of the delivery chain considers the delivery of goods and services to customers within a specific time interval. Nowadays, organizations are focusing to satisfy their customers’ demands not only to meet the expectations for products quality but also in delivery times through managing delivery chains. Obviously it is desirable that a company has minimum delivery time of goods and services to its customers. Therefore, establishing economic and reliable control charts for monitoring the key characteristics of delivery chain is of great importance especially for managers to improve the whole delivery chains performance. On the other hand, as we shall see in the present paper, the performance of a delivery chain is multivariate in nature because customers do not evaluate a delivery performance with a univariate mindset and also there are usually several production and delivery sites, and variety of different methods of transportation of goods and services. In this paper, we propose a relatively new application of the economic statistical design of the multivariate T2 control chart to monitor the delivery chain performance and it is illustrated through a case study in the TNT express mail in Iran. [less ▲]

Double Objective Economic Statistical Design of the VPT2 Control Chart: Wald’s identity approach

E-print/Working paper (n.d.)

Recent studies have shown that applying the control chart by using a variable parameters (VP) scheme yields more rapid detection of assignable causes than the classical method of taking fixed sample sizes ... [more ▼]

Recent studies have shown that applying the control chart by using a variable parameters (VP) scheme yields more rapid detection of assignable causes than the classical method of taking fixed sample sizes at fixed intervals of time. In this paper, the problem of economical statistical design of the VP T2 control chart is considered as a double-objective minimization problem with the statistical objective adjusted average time to signal and the economic objective expected cost per hour. Then we strive to find the Pareto-optimal designs in which the two objectives are met simultaneously by using a multi-objective Genetic Algorithm or GA. Through an illustrative example, we show that relatively large benefits accrue to the VP method relative to the classical policy; further another advantage of our approach is to provide a list of alternative solutions that can be explored graphically. This then ensures flexibility and adaptability, an important attribute of contemporary control chart design. [less ▲]

Control charts in a delivery chain framework

E-print/Working paper (n.d.)

We call attention to delivery chain systems as an area for statistical process control research and propose using elapsed time variables as delivery-quality measures. We propose a Shewhart-style control ... [more ▼]

We call attention to delivery chain systems as an area for statistical process control research and propose using elapsed time variables as delivery-quality measures. We propose a Shewhart-style control charting strategy that we term ‘bundling’ which describes creating and averaging related time variables to allow for a reduction in the number of charts needed for monitoring delivery chain systems. The major assumption is that several related delivery chain system time-variables (DCSTV) representing origin to destination pairs that deliver products to a common geographical region would shift together when being monitored for delay. In the context of strategic monitoring of aggregate systems, bundled charts can effectively signal when origin-destination pairs shift in a particular direction. Given that some of the DCSTV can be ‘bundled’ for representation on Shewhart charts, decision makers can be provided an accurate assessment of the predictability (or unpredictability) of a delivery chain. Providing more accurate promises of delivery time through the use of Shewhart-style charts will ultimately reduce levels of safety stock which results in a reduction in inventory holding costs. [less ▲]

Economic Statistical Design of T2 Control Chart with Variable Sampling Intervals

E-print/Working paper (n.d.)

The usual procedure when employing a T2 control chart for process monitoring is to take samples of fixed size n0 every h0 hours from the process. Results are plotted and signals are investigated. Recent ... [more ▼]

The usual procedure when employing a T2 control chart for process monitoring is to take samples of fixed size n0 every h0 hours from the process. Results are plotted and signals are investigated. Recent studies have shown that using variable sampling intervals (VSI) rather than fixed sampling intervals (FRS) can help detect process shifts more quickly. In this paper, we build a model of a process controlled by a VSI T2 control chart so that users can determine economic statistical designs which are preferred to economic or statistical designs alone. This model allows us to explore the cost savings implications of VSI sampling. The cost model proposed by Lorenzen and Vance [13] is employed and we find optimal (minimum) costs using a genetic algorithm (GA) approach. [less ▲]