Phil Scarf

Phil Scarf
Cardiff University | CU · Cardiff Business School

PhD

About

134
Publications
70,449
Reads
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3,395
Citations
Citations since 2016
42 Research Items
1921 Citations
20162017201820192020202120220100200300400
20162017201820192020202120220100200300400
20162017201820192020202120220100200300400
20162017201820192020202120220100200300400
Additional affiliations
July 2020 - October 2020
Cardiff University
Position
  • Professor (Full)

Publications

Publications (134)
Article
We present a unified theory that posits three fundamental models as necessary and sufficient for modelling the bivariate scores in possessive ball-sports. These models provide the basis for perhaps more complicated models that can be used for prediction, experimentation, and explanation. First is the Poisson-match, for when goals are rare, or when...
Article
This paper describes the development of a decision support system (DSS) for evaluating membrane restoration strategy. The engine of the DSS is a digital twin (DT), a virtual representation of wear (degradation) and restoration of membrane elements in a reverse osmosis (RO) pressure vessel. The basis of the DT is a mathematical model that describes...
Chapter
This chapter provides some contributions for opportunistic maintenance optimization of multi-component system in the arising context of on-line monitoring and strong interactions between components. The key point is, on one hand, to model and integrate different kinds of dependencies (stochastic dependence, structural dependence and economic depend...
Chapter
Prognostics and health management can be described as an emerging engineering discipline which studies and associates the degradation processes to system lifecycle management. It allows for system health state assessment in real-time, as well as predicting its future health states. In this chapter we present a methodology that leads towards PHM of...
Chapter
Repair is a type of maintenance carried out on an item after it fails. A failure may occur any time, hence the times to repair cannot be pre-specified. Methods used to model times to failures are normally stochastic processes such as the renewal process and the homogeneous Poisson process, depending on the effectiveness of a repair. Apparently, the...
Article
Full-text available
This work studies outcome uncertainty and competitive balance from a broad perspective. It considers four sports with varying scoring rates, from soccer with typically three goals per match to netball with one hundred goals per match. Within a general modelling framework for a two-competitor contest, we argue that outcome uncertainty, the extent to...
Article
We introduce the binomial-match as a model for the bivariate score in a paired-contest. This model is naturally associated with sports in which the restart alternates following a goal. The model is a challenger to the Poisson-match, a pair of independent Poisson random variables whose means are related to the strengths of the competing teams. We us...
Article
We study an inspection and replacement policy for a system when maintenance actions are executed at times or “visits” with a fixed, periodic schedule. Then, the novel focus of the paper is not when to schedule maintenance but what maintenance to schedule at known times. Violations (defaults) may occur because time or resource is limited. The model...
Article
Models derived from distributions of order-statistics are useful for modelling ranked data. The well-known Bradley–Terry (BT) and Plackett–Luce (PL) models can be derived from the order statistics of the exponential distribution but cannot handle ties. However, ties often occur in sports, and the ability to accommodate them leads to more useful ran...
Article
This paper models age replacement and block replacement when there is the possibility of defaulting on the planned maintenance. A default occurs when a planned preventive replacement is not executed, and we discuss how defaults can arise in practice. Our aim is to study the robustness of block replacement and age replacement, bearing in mind that (...
Article
We investigate how the network position of organisations in an extended supply chain network impacts their financial performance. The paper argues that performance measurement tools should incorporate a network (external, connectedness) perspective in addition to an internal financial perspective. We merge local networks of companies in a supply ch...
Article
Full-text available
To this day, continuous developments of technical systems and increasing reliance on equipment have resulted in a growing importance of effective maintenance activities. During the last couple of decades, a substantial amount of research has been carried out on this topic. In this study we review more than two hundred papers on maintenance modeling...
Article
Novel models of imperfect repair are fitted to classic reliability datasets. The models suppose that a virtual system comprises a component and a remainder in series. On failure of the component, the component is renewed, and on failure of the remainder, the component is renewed and the remainder is minimally repaired. It follows that the repair pr...
Article
We model the inspection-maintenance of a critical system in which the execution of inspections is random. The models we develop are interesting because they mimic realities in which production is prioritised over maintenance, so that inspections might be impeded or they might be opportunistic. Random maintenance has been modelled by others but ther...
Article
Full-text available
This paper proposes a model of inspection of a protection system in which the inspection outcome provides imperfect information of the state of the system. The system itself is required to operate on demand typically in emergency situations. The purpose of inspection is to determine the functional state of the system and consequently whether the sy...
Preprint
We suppose that performance is a random variable whose expectation is related to training inputs, and we study four performance measures in a statistical model that relates performance to training. Our aim is to carry out a robust statistical analysis of the training-performance models that are used in proprietary software to plan training, and the...
Article
This paper develops a model of a condition-based maintenance policy for a two-component system with both stochastic and economic dependencies. The stochastic dependency is such that the degradation rate of each component depends not only on its own state (degradation level) but also on the state of the other component. The economic dependency is su...
Article
The degradation process of complex multi-component systems is highly stochastic in nature. A major side effect of this complexity is that components of such systems may have unexpected reduced life and faults and failures that decrease the reliability of multi-component systems in industrial environments. In this work, we provide maintenance practi...
Article
In this paper we investigate the relationship between outcome uncertainty and scoring rates in the framework of a “Poisson match”. We argue that increasing scoring rates in the hope of increasing entertainment may have a detrimental impact on the popularity of sport. The basis of our argument is that higher scoring-rates decrease outcome uncertaint...
Article
We model a joint inspection and spare parts inventory policy for maintaining machines in a parallel system, where simultaneous downtime seriously impacts upon production performance and has a significant financial consequence. This dependency between system components means that analysis of realistic maintenance models is intractable. Therefore we...
Article
An inspection and replacement policy for a protection system is described by a mathematical model that incorporates multiple aspects of maintenance quality. A three-state component failure model is assumed, with a defective state preceding failure. The quality of maintenance intervention is modelled by supposing that inspections may misclassify def...
Article
In this paper we consider the inspection and maintenance of a two-component system with stochastic dependence. A failure of component 1 may induce the defective state in component 2 which in turn leads to its failure. A failure of component 1 and a defect in component 2 are detected by inspection. Our model considers a conditional inspection policy...
Article
This paper develops a simulation model to determine the cost-optimum inspection policy for a multi-line production system taking account of simultaneous downtime. The machines in the multi-line system are subject to a two stage failure process that is modelled using the delay-time concept. Our study indicates that: consecutive inspection of lines w...
Article
Full-text available
We model the influence of opportunities in a hybrid inspection and replacement policy. The base policy has two phases: an initial inspection phase in which the system is replaced if found defective; and a later wear-out phase that terminates with replacement and during which there is no inspection. The efficacy of inspection is modelled using the d...
Conference Paper
Complex mechatronic systems are becoming more widespread such as in industrial machinery and robotic systems. Detecting faults in such systems proves to be a challenging task due to the multitude of components that are interacting. In this paper, we demonstrate how we use an unsupervised learning technique to detect accelerated wear patterns in com...
Article
Full-text available
The development of the Poisson match as a model used in the prediction of the outcome of football matches is described. In this context, many interesting modelling projects arise that are suitable for undergraduate, final year students. In a narrative that discusses the author’s engagement with this model and other related models, the paper present...
Article
We develop a delay time model for a one component system with postponed replacement to analyze situations in which maintenance might not be executed immediately upon discovery of a defect in the system. Reasons for postponement are numerous: to avoid production disruption or unnecessary or ineffective replacement; to prepare for replacement; to ext...
Chapter
Soccer (or association football) is themost popular sport in theworld, with an estimated 3.5 billion fans and 250 million players worldwide (Sporty Desk, 2015). Betting on outcomes in soccer matches is also very popular, unsurprisingly, and the value of the soccer betting market in 2012 is estimated to be between £500 billion and £700 billion (Keog...
Conference Paper
This paper proposes a general deterioration model for a multi-component system. The deterioration process of a component depends upon the operational conditions, the component’s own state, and also the state of other components. An experimental platform that aims to provide more insight into the true nature of degradation of multi-component systems...
Article
Full-text available
Sequential regression approaches can be used to analyze processes in which covariates are revealed in stages. Such processes occur widely, with examples including medical intervention, sports contests and political campaigns. The naïve sequential approach involves fitting regression models using the covariates revealed by the end of the current sta...
Article
Consider a series system consisting of sockets into each of which a component is inserted: if a component fails, it is replaced with a new identical one immediately and system operation resumes. An interesting question is: how to model the failure process of the system as a whole when the lifetime distribution of each component is unknown? This pap...
Article
Full-text available
The cadence that maximises power output developed at the crank by an individual cyclist is conventionally determined using a laboratory test. The purpose of this study was two-fold: (i) to show that such a cadence, which we call the optimal cadence, can be determined using power output, heart-rate, and cadence measured in the field and (ii) to desc...
Conference Paper
Full-text available
The paper deals with a condition-based maintenance policy for a two-component system with dependencies. Two kinds of dependency are investigated. The first is state dependence whereby the deterioration speed of each component depends not only on its own state (deterioration level) but also on the state of the other. The second is economic dependenc...
Article
Full-text available
First, we would like to thank all authors for their excellent contributions to this special issue. Of course, sincere thanks go also to all reviewers for their careful (and voluntary) review work, which has helped to improve the quality of the papers published and thus the significance of the special issue.
Article
This paper considers an inspection and preventive replacement policy for a one-component protection or cold standby system. Inspection is imperfect, and subject to false positives and negatives; preventive replacement may also be of poor quality. We determine conditions relating to the quality of the inspection and preventive replacement under whic...
Article
Full-text available
In general, the evaluation of player performance in test cricket is based on measures such as batting and bowling averages. These measures have a number of limitations, among which is that they fail to take into account the context in which runs are made or conceded and wickets are taken or given away. Furthermore, batting and bowling averages do n...
Article
The failure processes of repairable systems may be impacted by operational and environmental stress factors. To accommodate such factors, reliability can be modelled using a multiplicative intensity function. In the proportional intensity model, the failure intensity is the product of the failure intensity function of the baseline system that quant...
Chapter
The specification of a maintenance design is at the heart of maintenance modeling and management. This design is essentially a structured description of the system of interest in terms of its parts (components, sockets, and their interrelationships), and prescribed maintenance rules for the components in the system. The maintenance rules are determ...
Article
Full-text available
This paper uses a statistical analysis of match sprint outcomes to guide tactical decisions in this highly tactical contest and to provide competitors and coaches with a potential, marginal gain. Logistic regression models are developed to predict the probability of the leading rider winning at different points of the race, based on how the race pr...
Article
Full-text available
This paper considers the effect of fleet size on a joint policy of maintenance and spare parts inventory when spare parts are of varying quality. We consider N identical one-component systems subject to age-based replacement, and with a single echelon periodic review spare-parts policy. The joint policy is optimised with regard to the long-run tota...
Article
Full-text available
This paper models imperfect inspection policies for a system with a finite operational time requirement. Two types of maintenance policy are considered: that in which an alarm (a positive inspection) is followed by a check of the validity of the alarm at additional cost, and if the system is good it continues in service and if failed it is retired;...
Article
In this paper, generalised estimators are proposed to estimate seasonal indices for certain forms of additive and mixed seasonality. The estimators combine one of two group seasonal indices methods—Dalhart's group method and Withycombe's group method—with a shrinkage method in different ways. Optimal shrinkage parameters are derived to maximise the...
Article
Full-text available
The EA Sports Player Performance Index is a rating system for soccer players used in the top two tiers of soccer in England—the Premier League and the Championship. Its development was a collaboration among professional soccer leagues, a news media association, and academia. In this paper, we describe the index and its construction. The novelty of...
Article
Full-text available
This paper forecasts match outcomes in test cricket in play, session by session. Match outcome probabilities at the start of each session are forecast using a sequence of multinomial logistic regression models. These probabilities can assist a team captain or management in considering a certain aggressive or defensive batting strategy for the comin...
Article
An inspection and replacement policy for a protection system is described in which the inspection process is subject to error, and false positives (false alarms) and false negatives are possible. We develop two models: one in which a false positive implies renewal of the protection system; the other not. These models are motivated by inspection of...
Article
Heterogeneity in component and maintenance quality is considered in the context of age-based inspection and replacement for a single component system. A three-state component failure model is assumed, with a defective state preceding the failed state. Heterogeneity in maintenance intervention is modelled by supposing that inspections may induce the...
Article
Full-text available
This paper analyses declaration and the follow-on decisions in test cricket. We model the match outcome given the end of first, second and third innings positions; data on 391 test matches, from the period 1997 to 2007, are used to fit the models. We then investigate how declaration strategy should vary from innings to innings, and how the nature a...
Article
The technique of machinery fault diagnosis has been greatly enhanced over recent years with the application of many pattern classification methods. However, these classification methods suffer from the “curse of dimensionality” when applied to high-dimensional fault diagnosis data. In order to solve the problem, this paper proposes a hybrid model w...
Chapter
Full-text available
This paper considers an inspection policy for a single component protection or preparedness system, in which the component arises from a heterogeneous population. At any point in time, the system may be in one of three states, good, defective or failed. The system is only required in an emergency, and in order to ensure high availability of the sys...
Article
This paper considers an inspection policy for a single component protection or preparedness system, in which the component arises from a heterogeneous population. At any point in time, the system may be in one of three states, good, defective or failed. The system is only required in an emergency, and in order to ensure high availability of the sys...
Article
Warranty extensions are considered for automotive vehicles. In particular, the expected cost to a manufacturer of an extension to a base warranty is determined, while taking account of the effect of services during the warranty period. To model the effect of services, an inspection maintenance model is used that is based on the delay time concept....
Article
Full-text available
This paper presents models for the number of goals scored by opposing teams in international soccer matches. The bivariate discrete distributions employed are defined in terms of the marginal distributions and a dependence copula. This copula representation allows dependence in the bivariate distribution to be modelled in a flexible manner by speci...
Article
Full-text available
  Negative binomial distributions are fitted to partnership scores and innings scores in test cricket. For partnership scores, we use a parametric model that allows us to consider run rate as a covariate in the distribution of runs scored and hence to use run rate as a surrogate for batting strategy. Then we describe the implied influence of run ra...
Article
Full-text available
Tournament outcome uncertainty depends on: the design of the tournament; and the relative strengths of the competitors – the competitive balance. A tournament design comprises the arrangement of the individual matches, which we call the tournament structure, the seeding policy and the progression rules. In this paper, we investigate the effect of s...
Article
More often than not, the results of experimental studies are reported in terms of averages, best-fit lines, confidence limits, and distribution functions. However, the most economically important use of statistics in corrosion is undoubtedly in the analysis of inspection results to estimate the corrosion rate of industrial plant. This chapter provi...
Article
Novel replacement policies that are hybrids of inspection maintenance and block replacement are developed for an n identical component series system in which the component parts used at successive replacements arise from a heterogeneous population. The heterogeneous nature of components implies a mixed distribution for time to failure. In these cir...
Chapter
Full-text available
During the third innings, we suppose that the batting team selects a run-rate and target to optimise the match outcome probabilities. Outcome probabilities are calculated using a model for the outcome given the end of third innings position, and a model for the target set given the current position and the chosen run-rate. While the run-rate is not...
Article
A two-phase inspection policy for a single component, preparedness system is investigated. Inspections or tests are considered to be imperfect; that is, false positives and false negatives can occur. We further suppose that a component may be weak or strong, with a lifetime distribution that follows a mixture. In these circumstances, the long-run c...
Article
This paper considers preventive maintenance for a single component from a heterogeneous population. Component heterogeneity is modeled by supposing that the lifetime of a component arises from a mixture distribution. The mixture distribution combines two distributions-one with short characteristic lifetime that represents a sub-population of weak c...