References of "Faraz, Alireza"
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See detailEconomic Statistical Design of the VP( X) ̅ Control Charts for Monitoring a Process under Non-normality
Seif, Asghar; Faraz, Alireza ULg; Saniga, Erwin

E-print/Working paper (2014)

Recent studies proved that variable parameters (VP) X ̅ control charts not only detects process mean shifts quicker than the classical X ̅ control chart but also has better economic properties ... [more ▼]

Recent studies proved that variable parameters (VP) X ̅ control charts not only detects process mean shifts quicker than the classical X ̅ control chart but also has better economic properties. Furthermore, like most papers in control chart design, the fundamental assumption is that process data are normally distributed. Nevertheless, process quality variables may not be normal in application. In this paper, we investigate the economic statistical design of the VP X ̅ control chart when the underlying process distribution is non-normal. We illustrate the design procedure and perform a sensitivity analysis on the process and cost parameters based upon the degrees of skewness and kurtosis of the population using an industrial application. [less ▲]

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See detailThe application of the NSGA-II optimization method in designing control charts
Faraz, Alireza ULg; Heuchenne, Cédric ULg; Seif, Asghar

Scientific conference (2014, June 04)

The problem of designing control chart is formulated as a multi-objective optimization problem with the adjusted average time to signal as the statistical objective and the expected cost per hour as the ... [more ▼]

The problem of designing control chart is formulated as a multi-objective optimization problem with the adjusted average time to signal as the statistical objective and the expected cost per hour as the economic objective. Then we try to find the Pareto-optimal designs in which the two objectives are minimized simultaneously by using the elitist non-dominated sorting genetic algorithm method. Through an illustrative example, the advantages of the proposed approach is shown by providing a list of viable optimal solutions and graphical representations, thereby bolding the advantage of flexibility and adaptability. [less ▲]

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See detailEvaluation of the Economic Statistical Design of the Multivariate T2 Control Chart with Multiple Variable Sampling Intervals Scheme: NSGA-II Approach
Faraz, Alireza ULg; Seif, Asghar; Sadeghifar

in Journal of Statistical Computation & Simulation (2014)

The economic and statistical merits of a multiple variable sampling intervals (MVSI) scheme are studied. The problem is formulated as a double-objective optimization problem with the adjusted average time ... [more ▼]

The economic and statistical merits of a multiple variable sampling intervals (MVSI) scheme are studied. The problem is formulated as a double-objective optimization problem with the adjusted average time to signal as the statistical objective and the expected cost per hour as the economic objective. Bai and Lee’s ‎[2] economic model is considered. Then we find the Pareto-optimal designs in which the two objectives are minimized simultaneously by using the non-dominated sorting genetic algorithm. Through an illustrative example, the advantages of the proposed approach is shown by providing a list of viable optimal solutions and graphical representations, which indicate the advantage of flexibility and adaptability of our approach. [less ▲]

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See detailThe Robust Economic Statistical Design of the Hotelling’s T^2 Chart
Faraz, Alireza ULg; Chalaki, Kamyar; Saniga, Erwin et al

in Journal of Statistical Computation & Simulation (2014)

Economic statistical designs aim at minimizing the cost of process monitoring when a specific scenario or a set of estimated process and cost parameters is given. However, in practical situations the ... [more ▼]

Economic statistical designs aim at minimizing the cost of process monitoring when a specific scenario or a set of estimated process and cost parameters is given. However, in practical situations the process may be affected by more than one scenario which may lead to severe cost penalties for upsetting the true scenario. This paper presents the robust economic statistical design (RESD) of the T^2 chart to reduce the monetary losses when there are multiple distinct scenarios. The genetic algorithm optimization method is employed here to minimize the total expected monitoring cost across all distinct scenarios. Through two numerical examples the proposed method is illustrated. Simulation studies indicate that the robust economic statistical designs should be encouraged in practice. [less ▲]

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See detailShewhart Control Charts for Monitoring Reliability with Weibull Lifetimes
Faraz, Alireza ULg; Saniga, Erwin; Heuchenne, Cédric ULg

in Quality and Reliability Engineering International (2014)

In this paper, 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 ... [more ▼]

In this paper, 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 ▲]

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See detailDouble Objective Economic Statistical Design of the VPT2 Control Chart: Wald’s identity approach
Faraz, Alireza ULg; Heuchenne, Cédric ULg; Saniga, Erwin et al

in Journal of Statistical Computation & Simulation (2014), 84

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 ▲]

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See detailStatistically Bundled Shewhart Control Charts for Monitoring Delivery Chains Systems
Foster, Earnest; Faraz, Alireza ULg; Heuchenne, Cédric ULg

E-print/Working paper (2014)

Continuous monitoring of Delivery Time variables by means of control charts in a delivery chain is a very recent application of Statistical Process Control (SPC) to the service sector. The aim of the ... [more ▼]

Continuous monitoring of Delivery Time variables by means of control charts in a delivery chain is a very recent application of Statistical Process Control (SPC) to the service sector. The aim of the proposed method is to provide supply chain decision makers with an easy to be managed tool monitoring the current functioning state of the delivery chain. The implementation of SPC control charts makes it possible to limit over-corrections to false alarm conditions and to maintain at an acceptable level the safety stock, with a consequent reduction of the overall management costs of the delivery chain. An illustrative example shows the proposed control chart implementation in a real delivery chain. [less ▲]

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See detailA Statistically adaptive sampling policy to the Hotelling's T2 Control Chart: Markov Chain Approach
Seif, A.; Faraz, Alireza ULg; Heuchenne, Cédric ULg et al

in Communications in Statistics : Theory & Methods (2014)

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See detailDouble-objective Economic Statistical Design of the Adaptive T2 Control Charts
Faraz, Alireza ULg; Heuchenne, Cédric ULg; Saniga, Erwin et al

Conference (2013, July 09)

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See detailMonitoring delivery chains using multivariate control charts
Faraz, Alireza ULg; Heuchenne, Cédric ULg; Saniga, Erwin 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 ▲]

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See detailThe variable parameters T2 chart with run rules
Faraz, Alireza ULg; Celano, Giovanni; Heuchenne, Cédric ULg et al

in Statistical Papers (2013)

The Hotelling’s T2 control chart with variable parameters (VP T2) has been shown to have better statistical performance than other adaptive control schemes in detecting small to moderate process mean ... [more ▼]

The Hotelling’s T2 control chart with variable parameters (VP T2) has been shown to have better statistical performance than other adaptive control schemes in detecting small to moderate process mean shifts. In this paper, we investigate the statistical performance of the VP T2 control chart coupled with run rules. We consider two well-known run rules schemes. Statistical performance is evaluated by using a Markov chain modeling the random shock mechanism of the monitored process. The in-control time interval of the process is assumed to follow an exponential distribution. A Genetic Algorithm has been designed to select the optimal chart design parameters. We provide an extensive numerical analysis indicating that the VP T2 control chart with run rules outperforms other charts for small sizes of the mean shift expressed through the Mahalanobis distance. [less ▲]

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See detailMultiobjective Genetic Algorithm Approach to the Economic Statistical Design of Control Charts with an application to Xbar and S2 charts
Faraz, Alireza ULg; Saniga, Erwin

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 ▲]

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See detailControl Charts monitoring product’s loss to society
Celano, Giovanni; Faraz, Alireza ULg; Saniga, Erwin

in Quality and Reliability Engineering International (2013)

Taguchi introduced a new philosophy in quality control that accounts for the economic loss associated to process variation measured by deviations from the target value of a product quality characteristic ... [more ▼]

Taguchi introduced a new philosophy in quality control that accounts for the economic loss associated to process variation measured by deviations from the target value of a product quality characteristic. The Taguchi loss function has been considered in the design of control charts only for the computation of costs associated with nonconformities. This paper considers sample statistics based on the Taguchi loss function as a means to implement Shewhart control charts monitoring both the deviation from the target and dispersion of normally distributed quality characteristics. The aim of this proposed control chart is to perform on-line quality control of a process by monitoring its quality loss cost performance over time. To compute the quality loss performance, we consider a nominal-the-best quality characteristic. The statistical performance of the proposed control charts has been evaluated and compared with that of widely used control charts. Implementing target costing philosophy by means of one of the proposed charts is also discussed. An example illustrates the Taguchi control chart in a practical implementation. [less ▲]

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See detailStatistical performance of a control chart monitoring the ratio of two normal variables
Celano, Giovanni; CASTAGLIOLA, Philippe; Faraz, Alireza ULg et al

in Quality and Reliability Engineering International (2013)

On-line Statistical Process Control (SPC) monitoring the ratio Z of two normal variables X and Y has surprisingly received too little attention in the quality control literature. Several potential ... [more ▼]

On-line Statistical Process Control (SPC) monitoring the ratio Z of two normal variables X and Y has surprisingly received too little attention in the quality control literature. Several potential applications dealing with monitoring the ratio Z can be found in the industrial sector, when quality control of products consisting of several raw materials calls for monitoring the stability of the proportions (ratios) of different components within a product. Tables about the sensitivity of these charts in the detection of one or more assignable causes are still not available. This paper investigates the statistical performance of Phase II Shewhart control charts monitoring the ratio of two normal variables in the case of individual observations. The obtained results show that the performance of the proposed charts is a function of the distribution parameters of the two normal variables. In particular, the Shewhart chart monitoring the ratio Z outperforms the (p=2) multivariate  control chart when a process shift affects the in-control mean of X or, alternatively, of Y and the correlation among X and Y is high and when the in-control means of X and Y shift contemporarily to opposite directions. The sensitivity of the proposed chart to a shift of the in-control dispersion has been investigated, too. We also show that the standardization of the two variables before computing their ratio is not a good practice due to a significant loss in the chart’s statistical sensitivity. An illustrative example from the food industry is detailed to show the implementation of these control charts. [less ▲]

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See detailOptimal T2 control chart with double sampling scheme - an alternative to the MEWMA chart
Faraz, Alireza ULg; Heuchenne, Cédric ULg; Saniga, Erwin

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 ▲]

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See detailA modified economic-statistical design of the VP multivariate control charts
SEIF, Asghar; Faraz, Alireza ULg

Scientific 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 ▲]

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See detailOn the advantages of economically designed the Hotelling’s T2 control chart with variable sample sizes and sampling intervals
Faraz, Alireza ULg; kazemzadeh, R. B.; Parsian, Ahmad 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 ▲]

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See detailA Meta Model to Optimally Design the VSI T2 Control Chart
Faraz, Alireza ULg; Seif, A.

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 ▲]

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See detailThe Economic and Statistical Designs of Control charts for Censored and Non-Normal Data
Faraz, Alireza ULg; Heuchenne, Cédric ULg; Davis, Darwin, Edward 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 ▲]

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See detailA modified economic-statistical design of the T2 control chart with variable sample sizes and control limits
Seif, A.; Faraz, Alireza ULg; Heuchenne, Cédric ULg 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: 102 (31 ULg)