Benjamin P. H. Kemper

A Computational approach to optimized appointment scheduling

Appointment scheduling is prevalent in various healthcare settings. Generally, the objective is to determine a schedule (i.e., the sequence of epochs at which the individual patients are asked to appear) that appropriately balances the interests of the patients (low waiting times) and the medical staff (low idle times). In queueing language, the planner is given the distributions of the service times of the individual clients, and then it is his task to determine the arrival epochs of the clients. In this paper, we demonstrate how to generate schedules that have certain optimality properties. As a general principle, we express the performance of a schedule in terms of its associated utility, which incorporates both waiting times and idle times. In a first class of schedules (referred to as the simultaneous approach), the arrival epochs are chosen such that the sum of the utilities of all clients as well as the service provider is minimized. In a second class (sequential approach), the arrival epoch of the next client is scheduled, given the scheduled arrival epochs of all previous clients. For general service times the numerical evaluation of the optimal schedules is often prohibitive; it essentially requires knowledge of the waiting-time distribution in an appropriately chosen D/G/1 queue. In this paper, we demonstrate that by using the phase-type counterparts of the service-time distributions, it is feasible to efficiently determine an optimized schedule, that is, we obtain accurate results with low computational effort. We do so both for transient scenarios (in which the number of clients is relatively low, so that the interarrival time is not uniform) and stationary scenarios (with many clients, and essentially constant interarrival times). Our approach is backed by several examples, that give insight in the impact of the variability of the service times on the schedule; it also shows the impact of the utility function selected.

Optimized appointment scheduling

In service systems, in order to balance the server’s idle times and the customers’ waiting times, one may fix the arrival times of the customers beforehand in an appointment schedule. We propose a procedure for determining appointment schedules in such a D/G/1-type of system by sequentially minimizing the per-customer expected loss. Our approach provides schedules for any convex loss function; for the practically relevant cases of the quadratic and absolute value loss functions appealing closed-form results are derived. Importantly, our approach does not impose any conditions on the service time distribution; it is even allowed that the customers’ service times have different distributions.

Generic Lean Six Sigma project definitions in publishing

Purpose – Many companies in the publishing industry are facing the task of developing new business models and becoming more efficient and effective in execution. Lean Six Sigma (LSS) is a unified framework for systematically developing efficiency and quality improvements; it can help realize significant results and breakthrough improvements in the publishing industry, as demonstrated with many projects from a Dutch multinational publishing company. The purpose of this paper is to facilitate the process of defining LSS projects in publishing, because lack of a clear definition is an important cause for project failure.Design/methodology/approach – The paper discusses and categorizes 49 project definitions based on two elements: the critical to quality flowdown and the corresponding set of operational definitions and shows how this simple categorization and subsequent standardization of approaches can help LSS teams simplify the definition phase.Findings – The strategy presented in this paper provides seven...

Modeling process flow using diagrams

In the practice of process improvement, tools such as the flowchart, the value-stream map (VSM), and a variety of ad hoc variants of such diagrams are commonly used. The purpose of this paper is to present a clear, precise, and consistent framework for the use of such flow diagrams in process improvement projects. The paper finds that traditional diagrams, such as the flowchart, the VSM, and OR-type of diagrams, have severe limitations, miss certain elements, or are based on implicit but consequential premises. These limitations restrict the applicability of traditional diagrams in non-manufacturing areas such as service and healthcare processes. We show that a rational reconstruction for the use of diagrams in various disciplines regarding process flow boils down to a generic framework of elements, definitions of generic process metrics, and three classes of applications, namely the ‘as-is’, ‘could-be’, and ‘should-be’ analysis. The goal is not to replace all currently used diagrams, but merely to discuss the role of diagram usage in process flow modeling. This paper provides an explicit framework that is unambiguous and flexible, and has the potential to serve as a guideline for the practitioner, in manufacturing as well as in service and healthcare. Besides, it may serve as a starting point to develop an ontology of business processes.

Principles of Exploratory Data Analysis in Problem Solving: What Can We Learn from a Well-Known Case?

ABSTRACT Exploratory data analysis (EDA) is sometimes suggested as a hypothesis identification approach. It is often used as such in problem solving and consists of the analysis of observational data, often collected without well-defined hypotheses, with the purpose of finding clues that could inspire ideas and hypotheses. This article seeks to uncover some of the main principles of EDA in problem solving. The article discusses and explains EDAs main steps: (1) Display the data; (2) identify salient features; (3) interpret salient features. The empiricist notion of EDA, which pervades many textbook accounts of EDA, is criticized and contrasted to an account that emphasizes the role of mental models in hypothesis generation. The framework has some implications for the limitations of EDA. It also sheds light on the role of the statistician compared to the role of the context expert. The article argues that in teaching EDA the emphasis for statistical data analysis should be balanced with teaching students to theorize and be inquisitive. Throughout the article, ideas are illustrated by the well-known case of John Snows studies of the transmission mechanism of cholera.

A study on how to improve the throughput time of Lean Six Sigma projects in a construction company

Purpose – The purpose of this paper is to study the use of the Lean Six Sigma (LSS) methodology in a construction company. Design/methodology/approach – In our study we analyze 62 LSS improvement projects carried out within a Dutch company. In our analysis we focus on both speed, in terms of throughput time (THT), and impact, in terms of project completion, of each project. Findings – From the analysis we conclude that the current THT of a project is about a year and we identify important factors that cause large projects THTs These factors are then translated into recommendations for an efficient execution of LSS improvement projects. Research limitations/implications – The analysis is based on a sample from one company of the Dutch construction industry. The scope should be broadened as more companies adopt quality and process improvement programs, such as LSS. Originality/value – The narrowed scope, only one company and focused mostly on the speed of projects, helped to do an in-depth analysis. Theref...

Mean sojourn times in two-queue fork-join systems: bounds and approximations

This paper considers a fork-join system (or: parallel queue), which is a two-queue network in which any arrival generates jobs at both queues and the jobs synchronize before they leave the system. The focus is on methods to quantify the mean value of the ‘system’s sojourn time’ S: with Si denoting a job’s sojourn time in queue i, S is defined as max{S1, S2}. Earlier work has revealed that this class of models is notoriously hard to analyze. In this paper, we focus on the homogeneous case, in which the jobs generated at both queues stem from the same distribution. We first evaluate various bounds developed in the literature, and observe that under fairly broad circumstances these can be rather inaccurate. We then present a number of approximations, that are extensively tested by simulation and turn out to perform remarkably well.

Optimal appointment scheduling in continuous time: The lag order approximation method

We study appointment scheduling problems in continuous time. A finite number of clients are scheduled such that a function of the waiting time of clients, the idle time of the server, and the lateness of the schedule is minimized. The optimal schedule is notoriously hard to derive within reasonable computation times. Therefore, we develop the lag order approximation method, that sets the client’s optimal appointment time based on only a part of his predecessors. We show that a lag order of two, i.e., taking two predecessors into account, results in nearly optimal schedules within reasonable computation times. We illustrate our approximation method with an appointment scheduling problem in a CT-scan area.

Quality Quandaries: The Availability of Infusion Pumps in a Hospital

A case study illustrates the application of Lean Six Sigma to healthcare in The Netherlands. The specific case involves reducing operational costs of infusion pumps in a general hospital. A background is provided, followed by a discussion of some of the..

Quality quandaries: Streamlining the path to optimal care for cardiovascular patients

The Quality Quandaries column highlights a lean Six Sigma improvement project in a Netherlands hospitals cardiology department.