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A Statistically adaptive sampling policy to the Hotelling's T2 Control Chart: Markov Chain Approach ; Faraz, Alireza ; Heuchenne, Cédric et al in Communications in Statistics : Theory & Methods (2014) Detailed reference viewed: 37 (4 ULg)Characteristics of Economically Designed CUSUM and \bar{X} Control Charts ; ; Faraz, Alireza et al Conference (2013, August 22) In this paper we investigate the characteristics of economic control chart designs for both Shewhart (¯X ) and CUSUM control charts. Authors in the past have made some suggestions regarding the design of ... [more ▼] In this paper we investigate the characteristics of economic control chart designs for both Shewhart (¯X ) and CUSUM control charts. Authors in the past have made some suggestions regarding the design of these charts, where design is defined as finding the values of sample size, intersample interval and control limit (Shewhart chart) or control parameters (k and h) for the CUSUM chart. Here, we run a large number of experiments consisting of many configurations of the parameters and describe and model the results in terms of the actual economic designs. [less ▲] Detailed reference viewed: 15 (1 ULg)Double-objective Economic Statistical Design of the Adaptive T2 Control Charts Faraz, Alireza ; Heuchenne, Cédric ; et al Conference (2013, July 09) Detailed reference viewed: 30 (4 ULg)Monitoring delivery chains using multivariate control charts Faraz, Alireza ; Heuchenne, Cédric ; et al in European Journal of Operational Research (2013), 228(1), 282289 Delivery chains are concerned with the delivery of goods and services to customers within a specific time interval; this time constraint is added to the usual consumer demand for product or service ... [more ▼] Delivery chains are concerned with the delivery of goods and services to customers within a specific time interval; this time constraint is added to the usual consumer demand for product or service quality. In this context, we address the idea of using process control tools to monitor this key variable of delivery time. In applications, there are usually several production and delivery sites and a variety of different ways to transport, treat and provide goods and services; that makes the problem multivariate in nature. We therefore propose to control the process using multivariate T2 control charts economically designed with the addition of statistical constraints, a design method called economic-statistical design. We illustrate the application in general through an illustrative example. [less ▲] Detailed reference viewed: 145 (31 ULg)Monitoring distribution networks in supply chains Faraz, Alireza Conference (2013, May 17) This paper presents a new control chart for monitoring the post optimality of a designed distribution network in a supply chain. The proposed control chart alarms as soon as neither the location nor the ... [more ▼] This paper presents a new control chart for monitoring the post optimality of a designed distribution network in a supply chain. The proposed control chart alarms as soon as neither the location nor the capacity nor the number of the current distribution centers are not optimal any longer. The control chart ensures the distribution network satisfies the customers' demands at minimum total costs over time. In fact, it monitors the optimality of the solution today for the problem tomorrow. [less ▲] Detailed reference viewed: 10 (0 ULg)Multiobjective Genetic Algorithm Approach to the Economic Statistical Design of Control Charts with an application to Xbar and S2 charts Faraz, Alireza ; in Quality and Reliability Engineering International (2013), 29(3), 407-415 Control charts are the primary tools of statistical process control. These charts may be designed by using a simple rule suggested by Shewhart, by a statistical criterion, an economic criterion or a joint ... [more ▼] Control charts are the primary tools of statistical process control. These charts may be designed by using a simple rule suggested by Shewhart, by a statistical criterion, an economic criterion or a joint economic-statistical criterion. Each method has its strengths and weaknesses. One weakness of the methods of design listed above is their lack of flexibility and adaptability, a primary objective of practical mathematical models. In this paper, we explore multi objective models as an alternative for the methods listed above. These provide a set of optimal solutions rather than a single optimal solution and thus allow the user to tailor their solution to the temporal imperative of a specific industrial situation. We present a solution to a well known industrial problem and compare optimal multi objective designs to economic designs, statistical designs, economic statistical designs and heuristic designs. [less ▲] Detailed reference viewed: 85 (13 ULg)Optimal T2 control chart with double sampling scheme - an alternative to the MEWMA chart Faraz, Alireza ; Heuchenne, Cédric ; in Quality and Reliability Engineering International (2012), 28(7), 751-760 Recent studies have shown that the double sampling (DS) scheme yields rapid detection of out of control situations, but the economic consequences of applying the proposed method are not discussed in the ... [more ▼] Recent studies have shown that the double sampling (DS) scheme yields rapid detection of out of control situations, but the economic consequences of applying the proposed method are not discussed in the literature yet. In this paper, the economic statistical design of the DS T2 control chart is designed to address this issue. In this regard, upon the Lorenzen and Vance (1986)’s economic model, the problem is formulized and then the cost function is minimized using the genetic algorithm search method to obtain the optimal design parameters. Besides, we assumed that the length of the time that process remains in control is exponentially distributed. Through an illustrative example we show that by applying the proposed method relatively large benefits can be achieved in a comparison with the classical T2 and the statistical DS T2 charts. Furthermore the performance of the ESD DS T2 charts is compared to the MEWMA and other variable ratio sampling (VRS) T2 control charts in the literature. [less ▲] Detailed reference viewed: 84 (23 ULg)A modified economic-statistical design of the VP multivariate control charts ; Faraz, Alireza Conference (2012, January 15) Hotelling’s T2 control chart is one of the most popular multivariate control charts for monitoring multiple variables simultaneously. Recent studies have shown that applying the T2 control chart by using ... [more ▼] Hotelling’s T2 control chart is one of the most popular multivariate control charts for monitoring multiple variables simultaneously. Recent studies have shown that applying the T2 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. This paper presents an economic-statistical design (ESD) of the VP T2 control chart using the general model of Lorenzen and Vance. The genetic algorithm (GA) is then employed to search for the optimal values of the eight test parameters of the chart. Furthermore, VP and FRS schemes are compared with respect to the expect cost per unit time. [less ▲] Detailed reference viewed: 39 (3 ULg)On the advantages of economically designed the Hotelling’s T2 control chart with variable sample sizes and sampling intervals Faraz, Alireza ; ; et al in Quality & Quantity (2012), 46(1), 39-53 Faraz and Parsian (Statistical Paper, 47: 569–593, 2006) have shown that the double warning lines (DWL) scheme detects process shifts more quickly than the other variable ratio sampling schemes such as ... [more ▼] Faraz and Parsian (Statistical Paper, 47: 569–593, 2006) have shown that the double warning lines (DWL) scheme detects process shifts more quickly than the other variable ratio sampling schemes such as variable sample sizes (VSS), variable sampling intervals (VSI) and variable sample sizes and sampling intervals (VSSVSI). In this paper, the DWLT2control chart for monitoring the process mean vector is economically designed. The cost model proposed by Costa and Rahim (Journal of Applied Statistics, 28: 875–885, 2001) is used here and is minimized through a genetic algorithm (GA) approach. Then the effects of the model parameters on the chart parameters and resulting operating loss is studied and finally a comparison between all possible variable ratio sampling (VRS) schemes are made to choose the best option economically. [less ▲] Detailed reference viewed: 60 (16 ULg)A Meta Model to Optimally Design the VSI T2 Control Chart Faraz, Alireza ; in international Journal of Applied Operational Research (2012), 1(3), 53-69 Recent studies have shown that the variable sampling interval (VSI) scheme helps practitioners to detect process shifts more quickly than the classical scheme (FRS). In this paper, the economically and ... [more ▼] Recent studies have shown that the variable sampling interval (VSI) scheme helps practitioners to detect process shifts more quickly than the classical scheme (FRS). In this paper, the economically and statistically optimal design of the VSI T2 control chart for monitoring the process mean vector is investigated. The cost model proposed by Lorenzen and Vance [1] based on the Markov chain approach is modified as the objective function which is intended to be minimized through a genetic algorithm (GA) approach. Then, the effects of the costs and operating parameters on the optimal design (OD) of the chart parameters; and resulting operating loss through a fractional factorial design is systematically studied and finally, based on the ANOVA results, a Meta model to facilitate implementation in industry is proposed to determine the OD of the VSI T2 control chart parameters from the process and cost parameters. [less ▲] Detailed reference viewed: 22 (5 ULg)Economic Design of Control Charts In Presence of Censored Data Faraz, Alireza ; Heuchenne, Cédric Speech/Talk (2011) we present Shewhart type Z ̅ and S2 control charts for monitoring individual or joint shifts in the scale and shape parameters of a Weibull distributed process. The advantage of this method is its ease of ... [more ▼] we present Shewhart type Z ̅ and S2 control charts for monitoring individual or joint shifts in the scale and shape parameters of a Weibull distributed process. The advantage of this method is its ease of use and flexibility for the case where the process distribution is Weibull, although the method can be applied to any distribution. We illustrate the performance of our method through simulation and the application through the use of an actual data set. Our results indicate that Z ̅ and S2 control charts perform well in detecting shifts in the scale and shape parameters. We also provide a guide that would enable a user to interpret out-of-control signals. [less ▲] Detailed reference viewed: 14 (0 ULg)The Economic and Statistical Designs of Control charts for Censored and Non-Normal Data Faraz, Alireza ; Heuchenne, Cédric ; et al Scientific conference (2011, December) In this research, we are dealing with constructing the statistical design (SD) and economic statistical design (ESD) of Shewhart and CUSUM control charts for reliability data which are right censored ... [more ▼] In this research, we are dealing with constructing the statistical design (SD) and economic statistical design (ESD) of Shewhart and CUSUM control charts for reliability data which are right censored. This is the case which happens more frequently in the field. [less ▲] Detailed reference viewed: 39 (1 ULg)A modified economic-statistical design of the T2 control chart with variable sample sizes and control limits ; Faraz, Alireza ; Heuchenne, Cédric et al in Journal of Applied Statistics (2011), 38(11), 2459-2469 Recent studies have shown that using variable sampling size and control limits (VSSC) schemes result in charts with more statistical power than variable sampling size (VSS) when detecting small to ... [more ▼] Recent studies have shown that using variable sampling size and control limits (VSSC) schemes result in charts with more statistical power than variable sampling size (VSS) when detecting small to moderate shifts in the process mean vector. This paper presents an economic-statistical design (ESD) of the VSSC T2 control chart using the general model of Lorenzen and Vance [22]. The genetic algorithm approach is then employed to search for the optimal values of the six test parameters of the chart. We then compare the expected cost per unit of time of the optimally designed VSSC chart with optimally designed VSS and FRS (fixed ratio sampling) T2 charts as well as MEWMA charts. [less ▲] Detailed reference viewed: 108 (31 ULg)Statistical Merits and Economic Evaluation of T2 Control Charts with the VSSC Scheme ; ; Faraz, Alireza et al in Arabian Journal for Science and Engineering (2011), 36(7), 1461-1470 T2 control charts are used to monitor a process when more than one quality variable associated with the process is being observed. Recent studies have shown that using variable sampling size (VSS) schemes ... [more ▼] T2 control charts are used to monitor a process when more than one quality variable associated with the process is being observed. Recent studies have shown that using variable sampling size (VSS) schemes results in charts with more statistical power for detecting small to moderate shifts in the process mean vector. This paper presents an economic-statistical design of T2 control charts with variable sample size and control limits (VSSC). We build a cost model of a VSSC T2 control chart for the purpose of economic-statistical design using the model of Costa and Rahim (J. Appl. Stat. 28:875–885, 2001). This cost model constructed involves the cost of false alarms, the cost of finding and eliminating an assignable cause, the cost associated with production in an out-of-control state, and the cost of sampling and testing. We optimize this model using a genetic algorithm approach. Furthermore, VSSC and VSS T2 charts are compared with respect to the expected cost per unit time. [less ▲] Detailed reference viewed: 75 (24 ULg)A unification and some corrections to Markov chain approaches to develop variable ratio sampling scheme control charts Faraz, Alireza ; in Statistical Papers (2011), 52(4), 799-811 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 ▲] Detailed reference viewed: 25 (7 ULg)MULTIOBJECTIVE DESIGN OF CONTROL CHARTS Faraz, Alireza ; Heuchenne, Cédric Conference (2011, September 24) Detailed reference viewed: 25 (5 ULg)Monitoring delivery chains in a supply chain using multivariate control charts Faraz, Alireza ; Heuchenne, Cédric ; et al Conference (2011, July 13) 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 ▲] Detailed reference viewed: 56 (8 ULg)On the properties of the hotelling’s T2 control chart with variable sampling intervals Faraz, Alireza ; ; in Quality & Quantity (2011), 45(3), 579-586 When T 2 control chart is used to monitor a process, it is usually assumed that the samples of size n0 is taken at constant intervals t0 . In this paper, we investigate the T 2 control chart for ... [more ▼] When T 2 control chart is used to monitor a process, it is usually assumed that the samples of size n0 is taken at constant intervals t0 . In this paper, we investigate the T 2 control chart for monitoring the process mean vector when the sampling intervals are variable. Recent studies have shown that the variable sampling interval (VSI) scheme helps practitioners detect process shifts more quickly than the classical scheme Fixed Ratio Sampling (FRS). In this paper, it is assumed that the length of time the process remains in control is exponentially distributed. [less ▲] Detailed reference viewed: 42 (7 ULg)Economic Statistical Design of a T2 Control Chart with Double Warning Lines Faraz, Alireza ; in Quality and Reliability Engineering International (2011), 27(2), 125-139 Recent studies have shown that enhancing the common T2 control chart by using variable sample sizes (VSS) and variable sample intervals (VSI) sampling policies with a double warning line scheme (DWL ... [more ▼] Recent studies have shown that enhancing the common T2 control chart by using variable sample sizes (VSS) and variable sample intervals (VSI) sampling policies with a double warning line scheme (DWL) yields improvements in shift detection times over either pure VSI or VSS schemes in detecting almost all shifts in the process mean. In this paper, we look at this problem from an economical perspective, certainly at least as an important criterion as shift detection time if one considers what occurs in the industry today. Our method is to first construct a cost model to find the economic statistical design (ESD) of the DWL T2 control chart using the general model of Lorenzen and Vance (Technometrics 1986; 28:3–11). Subsequently, we find the values of the chart parameters which minimize the cost model using a genetic algorithm optimization method. Cost comparisons of Fixed ratio sampling, VSI, VSS, VSIVSS with DWL, and multivariate exponentially weighted moving average (MEWMA) charts are made, which indicate the economic efficacy of using either VSIVSS with DWL or MEWMA charts in practice if cost minimization is of interest to the control chart user. [less ▲] Detailed reference viewed: 51 (12 ULg)Economic and Economical Statistical Design of Hotelling’s T2 Control Chart with Two-State Adaptive Sample Size Faraz, Alireza ; ; in Journal of Statistical Computation & Simulation (2010), 80(12), 12991316 The Hotelling’s T 2 control chart, a direct analogue of the univariate Shewhart ¯X chart, is perhaps the most commonly used tool in industry for simultaneous monitoring of several quality characteristics ... [more ▼] The Hotelling’s T 2 control chart, a direct analogue of the univariate Shewhart ¯X chart, is perhaps the most commonly used tool in industry for simultaneous monitoring of several quality characteristics. Recent studies have shown that using variable sampling size (VSS) schemes results in charts with more statistical power when detecting small to moderate shifts in the process mean vector. In this paper, we build a cost model of a VSS T 2 control chart for the economic and economic statistical design using the general model of Lorenzen and Vance [The economic design of control charts: A unified approach, Technometrics 28 (1986), pp. 3–11].We optimize this model using a genetic algorithm approach.We also study the effects of the costs and operating parameters on theVSS T 2 parameters, and show, through an example, the advantage of economic design over statistical design forVSS T 2 charts, and measure the economic advantage of VSS sampling versus fixed sample size sampling. [less ▲] Detailed reference viewed: 79 (4 ULg) |
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