The objective of this work is to understand the dynamics of cryptocurrency prices. Specifically, how prices switch between different regimes, going from “bull” to “stable” and “bear” times. For this purpose, we propose a hidden Markov model that aims at explaining the evolution of Bitcoin prices through different, unobserved states. The implementation of the proposed model includes a likelihood ratio

Multivariate process capability indices (MPCIs) have been proposed to measure multivariate process capability in real‐world application over the past three decades. For the practitioner's point of view, the intention of this paper is to examine the performances and distributional properties of probability‐based MPCIs. Considering issues of construction of capability indices in multivariate setup and

The present study investigates the hybrid reliability modeling of structures in which the inputs contain both random variables and interval variables. Hybrid uncertainty is divided into three categories, including random variables mixed with random variables, interval variables mixed with interval variable, and random variables mixed with interval variables. In order to perform the reliability analysis

This article discusses the (precision and accuracy) relative efficiencies of all estimators of a normal population standard deviation σ = σ X for M > 1 subgroups of different sample sizes. We have examined the statistical properties of seven estimators of σ X which are (1) the pooled estimator S p, (2) the pooled unbiased estimator σ ^ pub , (3) the maximum likelihood estimator σ ^ mle , (4) Irving

On the basis of the principle of degradation mechanism invariance, a Wiener degradation process with random drift parameter is used to model the data collected from the constant stress accelerated degradation test. Small‐sample statistical inference method for this model is proposed. On the basis of Fisher's method, a test statistic is proposed to test if there is unit‐to‐unit variability in the population

Introduced robust density‐based estimators in the context of one‐shot devices with exponential lifetimes under a single stress factor. However, it is usual to have several stress factors in industrial experiments involving one‐shot devices. In this paper, the weighted minimum density power divergence estimators (WMDPDEs) are developed as a natural extension of the classical maximum likelihood estimators

mode and effects analysis (FMEA) is an effective tool to assess the risk of a system or process under uncertain environment. However, how to handle the uncertainty in the subjective assessment is an open issue. In this paper, a novel method to deal with the uncertainty coming from subjective assessments of FMEA experts is proposed in the framework of Dempster–Shafer evidence theory. First, the uncertain

A competing risks phenomenon arises in industrial life tests, where multiple types of failure determine the working duration of a unit. To model dependence among marginal failure times, copula models and frailty models have been developed for competing risks failure time data. In this paper, we propose a frailty‐copula model, which is a hybrid model including both a frailty term (for heterogeneity

To design the X ¯ control chart, the in‐control process mean and standard deviation must be estimated from historical samples, negatively affecting the chart's performance. The grand mean of a sample is the well‐established estimator for the process mean. However, regarding the standard deviation, the chart's user has at least five different estimators available in the literature to choose from. In

Monitoring the ratio between two random normal variables plays an important role in many industrial manufacturing processes. In this paper, we suggest designing two one‐sided Shewhart control charts monitoring this ratio. The numerical results show that the one‐sided charts have more advantages compared with the two‐sided Shewhart chart proposed previously in the literature. Moreover, we investigate

When designing control charts the in‐control parameters are unknown, so the control limits have to be estimated using a Phase I reference sample. To evaluate the in‐control performance of control charts in the monitoring phase (Phase II), two performance indicators are most commonly used: the average run length (ARL) or the false alarm rate (FAR). However, these quantities will vary across practitioners

No abstract is available for this article.

Evaluating the effect of measurement errors on either adaptive or simultaneous control charts has been a topic of interest for the researchers in the recent years. Nevertheless, the effect of measurement errors on both adaptive and simultaneous monitoring control charts has not been considered yet. In this paper, through extensive numerical studies, we evaluate the effect of measurement errors on an

For manufactured items sold by weight or volume, this article considers mixed acceptance criteria that put limits on the sample mean or on an upper confidence limit based on the sample mean and on the number of individual sample units that are nonconforming. For a normally distributed quality characteristic of interest, this article develops lower confidence limits for the mixed acceptance criteria

Product lifetime prediction is challenging when the product is subject to a time‐varying operational environment. Most of the existing studies use some functions to explicitly specify the relationship between degradation parameters and environmental conditions so as to reveal how the degradation process evolves over time. However, in many applications, the assumptions needed for establishing these

The first‐order reliability method (FORM) is well recognized as an efficient approach for reliability analysis. Rooted in considering the reliability problem as a constrained optimization of a function, the traditional FORM makes use of gradient‐based optimization techniques to solve it. However, the gradient‐based optimization techniques may result in local convergence or even divergence for the highly

In semiconductor manufacturing, wafer testing is performed to ensure the performance of each product after wafer fabrication. The wafer map is used to visualize the color‐coded wafer test results based on the locations. The defects on the wafer map may be randomly distributed or form clustered patterns. The various clustered defect patterns are usually caused by assignable faults. The identification

Rapid advancements in manufacturing technology have seen electronic products becoming lighter and thinner. This has led to production yield requirements of sawing processes in the semiconductor industry becoming increasingly strict. For sawing processes requiring a very low fraction of defective, the process capability index Cpk is widely applied for production yield measurement under the assumption

In phase I of statistical process control (SPC), control charts are often used as outlier detection methods to assess process stability. Many of these methods require estimation of the covariance matrix, are computationally infeasible, or have not been studied when the dimension of the data, p , is large. We propose the one‐class peeling (OCP) method, a flexible framework that combines statistical

Estimation of the parameters of generalized inverted exponential distribution is considered under constant stress accelerated life test. Besides the maximum likelihood method, nine different frequentist methods of estimation are used to estimate the unknown parameters. Moreover, the reliability function is estimated under use conditions based on different methods of estimation. We perform extensive

We investigate the challenges to be faced by quality practitioners to implement a control chart for individuals aimed at monitoring the stability of maximum/minimum realizations of profile quality features. We consider the situation where only a limited amount of inspections can be scheduled, which is typical of the most recent manufacturing applications for the production of small lots of customized

In this paper, we propose control charts for monitoring the Birnbaum‐Saunders (BS) median parameter (scale parameter) on the basis of three estimators. Comparison of the control charts in terms of average run length using probability control limits and those based on asymptotic distribution of three estimators for the median parameter is developed. We also present guidelines for practitioners about

Networked systems, such as telecommunications, transportation, and power transmission, are critical for the economic development and social well‐being of a society and are required to keep the prescribed demand continuously satisfied. Therefore, when planning maintenance actions for such a system, the adverse influence on its reliability caused by the unavailability of the components in the process

A unifying framework in defining and measuring resilience has been an intense research topic. In this paper, resilience is measured as a function of intrinsic capacities of a system, the effectiveness of recovery, and the extrinsic random shock process. Some existing resilience measures are analyzed as special cases of the proposed unifying measure. Then, we develop a framework in which the key constituents

Multivariable stochastic degradation system (MSDS) is quite common in industries such as blast furnace ironmaking, vehicle transportation, and aerospace manufacturing. Large‐scale complex equipments may be affected by multiple factors, resulting in not just a single deteriorating performance characteristic. It is difficult to handle unknown failure structures of practical systems by using traditional

We propose a distribution‐free cumulative sum (CUSUM) chart for joint monitoring of location and scale based on a Lepage‐type statistic that combines the Wilcoxon rank sum and the Mood statistics. Monte Carlo simulations were used to obtain control limits and examine the in‐control and out‐of‐control performance of the new chart. A direct comparison of the new chart was made with the original CUSUM

Two‐factor interactions, where the effect of one factor depends on the level of another factor, are common, and understanding them is often the key to solving quality problems or making process improvements using designed experiments. Resolution IV 2 k − p fractional factorial designs are efficient and require fewer experiments or runs than resolution V or full factorial experiments. However, two‐factor

The memory‐type control charts are quite efficient in monitoring small and moderate shifts in process parameters. These charts, such as exponentially weighted moving average (EWMA), face the problem of inertia due to the time dependence of statistics. This issue could be solved to some extent using a break at regular/irregular intervals in plotting statistics. We have proposed this method by introducing

Variation is an important phenomenon of the output of every manufacturing and production process. To deal with the natural and special cause variations in the process, quality practitioners mostly apply control charts. There have been regular advancements over time in the design structures of these charts such as runs rules, fast initial response, sampling mechanisms among many others. In this article

User experience is the focus of interaction design, and designing for errors is crucial for improving user experience. One method of designing for errors is to identify human errors and then initiate corrective actions on high‐risk errors to reduce their adverse effects. In this study, we proposed a hybrid approach for risk analysis of human error concerning user experience of interactive systems.

It is commonly recognized that software development is highly unpredictable and software quality may not be easily enhanced after software product is finished. During the software development life cycle (SDLC), project managers have to solve many technical and management issues, such as high failure rate, cost over‐run, low quality, and late delivery. Consequently, in order to produce robust and reliable

The aim of this paper is to highlight some concerns about the partly inaccurate manner in which the currently available 2‐of‐2 and 2‐of‐3 simple and improved runs‐rules charts based on the sign and the signed‐rank statistics were designed using Markov chain matrix. Because of the memory‐less property of the Markov chains, the empirical average run‐length (ARL) values were not affected; but the design

The prediction of remaining useful life (RUL) has attracted much attention, and it is also a key section for predictive maintenance. In this study, a novel hybrid deep learning framework is proposed for RUL prediction, where a variational autoencoder (VAE) and time‐window‐based sequence neural network (twSNN) are integrated. Among it, VAE is used to extract the hidden and low‐dimensional features from

Considered monitoring of the ratio of two correlated normal random variables based on an approximation. In this note, we derive a closed form expression for the ratio of two correlated normal random variables. We point out that the approximation used in Nguyen et al. does not always perform well.

An extended failure mode effect and criticality analysis (FMECA)‐based sample allocation method for testability verification is presented in this study to deal with the poor representativeness of test sample sets and the randomness of the testability evaluation results caused by unreasonable selection of failure samples. First, the fault propagation intensity is introduced as part of the extended information

This paper proposes two optimal control charts by using the generalized multiple dependent state (GMDS) plan to monitor the process mean. These charts make advantageous use of the ranked set sampling schemes and integrate them with the GMDS plan to improve the shift detection ability of the Shewhart‐type control charts. The proposed control charts have two pairs of control limits, inner and outer,

One of the modern statistical methods is assessing quality performance of product. The performance of a process in the manufacturing and services industry is assessed to examine the level of product quality. The product performance is measured using the lifetime performance index C L , where L is a lower specification limit. In this paper, the maximum likelihood estimation (MLE) of C L for the power

Emerge in technology brought well‐organized manufacturing systems to produce high‐quality items. Therefore, monitoring and control of products have become a challenging task for quality inspectors. From these highly efficient processes, produced items are mostly zero‐defect and modeled based on zero‐inflated distributions. The zero‐inflated Poisson (ZIP) and zero‐inflated Negative Binomial (ZINB) distributions

Traditional k‐out‐of‐n models assume that the components are independent, while recent research studies assume that the components are dependent caused by global load‐sharing characteristic. In this paper, we investigate the consecutive k‐out‐of‐n systems with dependent components by local load‐sharing characteristic. The work load and shock load on failed components will be equally shared by adjacent

The second edition of standard ISO 26262 (ed. 2018) for functional safety assessment in the automotive industry requires a hardware evaluation using the probabilistic metric for random hardware failures (PMHF). The standard for mentioned purpose highly recommends the fault tree analysis (FTA) utilization but does not give any specific calculation example. Therefore, this article describes computational

Quality engineers are increasingly faced with the need to deal with new types of data, which are significantly different from ordinary numerical data by virtue of their nature and the operations that can be performed with them. Basic concepts related to processing of such data, ie, data similarity, measurement system analysis, variation analysis, and data fusion, need to be thoroughly rethought. Reviewing

In the service and manufacturing industry, memory‐type control charts are extensively applied for monitoring the production process. These types of charts have the ability to efficiently detect disturbances, especially of smaller amount, in the process mean and/or dispersion. Recently, a new homogeneously weighted moving average (HWMA) chart has been proposed for efficient monitoring of smaller shifts

Robust design is an effective Quality by Design method to reduce product variation by selecting levels of design factors. For a number of situations, a nonstandard design region with linearly limited resources is needed to conduct an experiment. In the literature, little attention has been given to the development of robust design models for the nonstandard design region with a combination of linearly

Machine Learning (ML), or the ability of self‐learning computer algorithms to autonomously structure and interpret data, is a methodological approach to solve complicated optimization problems based on abundant data. ML is recently gaining momentum as algorithmic applications, computing potency, and available data sets increased manifold over the past two decades, providing an information‐rich environment

Components in many engineering and industrial systems can experience propagated failures, which not only cause the failure of the component itself but also affect other components, causing extensive damage to the entire system. However, in systems with functional dependence behavior where failure of a trigger component may cause other components (referred to as dependent components) to become unusable

Many reliability and maintenance decision problems need to estimate mean‐time‐to‐failure (MTTF) of a particular product component and/or build its life distribution model as early as possible based on field failure data. The field failure data are often heavily censored. In this case, the exponential‐assumption–based method can considerably overestimate the MTTF, and the classical parameter estimation