Faculty of Business

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The 39th international conference of the EURO working group on operational research applied to health services: ORAHS 2013 special issue
(Springer Science+Business Media, 2015-09) Çayırlı, Tuğba; Gunal, M. M.; Gunes, E.; Ormeci, L.; Business Administration; ÇAYIRLI, Tuğba
The healthcare sector is facing major challenges worldwide in terms of higher demands for efficiency, quality and equity. Operational Research (OR) techniques offer valuable tools for improving the design and delivery of healthcare services (e.g., inpatient and outpatient care, admission processes, emergency services, home healthcare, etc.), as well as improving the decision-making processes and implementation of public health policies.
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40th anniversary editorial: Looking backwards to move forward in management research
(Elsevier, 2022-08) Robinson, S.; Muratbekova-Touron, M.; Linder, C.; Bouncken, R. B.; Fındıkoğlu, Melike Nur; Garbuio, M.; Hartner-Tiefenthaler, M.; Thanos, I. C.; Aharonson, B. S.; Strobl, A.; Zhang, H.; Erz, A.; von Wallpach, S.; Karapinar, P. B.; Diedrich, A.; Saint-Germes, E.; Cole, R.; Management Information Systems; FINDIKOĞLU, Melike Nur
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Accelerated learning of user profiles
(Informs, 2011-02) Atahan, Pelin; Sarkar, S.; Sectoral Education and Professional Development; DEMİRCİLER, Pelin Atahan
Websites typically provide several links on each page visited by a user. Whereas some of these links help users easily navigate the site, others are typically used to provide targeted recommendations based on the available user profile. When the user profile is not available (or is inadequate), the site cannot effectively target products, promotions, and advertisements. In those situations, the site can learn the profile of a user as the user traverses the site. Naturally, the faster the site can learn a user's profile, the sooner the site can benefit from personalization. We develop a technique that sites can use to learn the profile as quickly as possible. The technique identifies links for sites to make available that will lead to a more informative profile when the user chooses one of the offered links. Experiments conducted using our approach demonstrate that it enables learning the profiles markedly better after very few user interactions as compared to benchmark approaches. The approach effectively learns multiple attributes simultaneously, can learn well classes that have highly skewed priors, and remains quite effective even when the distribution of link profiles at a site is relatively homogeneous. The approach works particularly well when a user's traversal is influenced by the most recently visited pages on a site. Finally, we show that the approach is robust to noise in the estimates for the probability parameters needed for its implementation.
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Accounting for age in marital search decisions
(Elsevier, 2016-06) Akın, Şerife Nuray; Platt, B. C.; Economics; DURAN, Şerife Nuray
Spouse quality, measured by educational attainment, varies significantly with the age at which an individual marries, peaking in the mid-twenties then declining through the early-forties. Interestingly, this decline is much sharper for women than men, meaning women increasingly marry less educated men as they age. Moreover, quality has worsened for educated women over several decades, while it has improved for men. Using a non-stationary sequential search model, we identify and quantify the search frictions that generate these age-dependent marriage outcomes. We find that single-life utility is typically the dominant friction, though college women in the 1950 and 1970 cohorts are affected even more by deteriorating suitor quality. Regardless of educational status, individual choice (as opposed to pure luck) is pivotal in explaining marriage market outcomes earlier in life.
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Action research contextualizes DEA in a multi-organizational decision-making process
(Elsevier, 2012-06-01) Oral, Muhittin; Business Administration; ORAL, Muhittin
The theory of participatory action research (PAR) grew out of the practice of problem-solving in groups and organization by involving the participation of all pertinent stakeholders in decision-making process through empowerment. The ontological assumption is that “the world out there” is defined by the participating stakeholders as they understand and perceive it. The actionable knowledge thus produced is mostly used subjectively in the hope of a favorable organizational change or a transformation for betterment. On the other hand, Management Science/Operations Research (MS/OR) is more concerned with epistemological objectivity in identifying and defining managerial issues and finding solutions. In this paper we shall show that MS/OR can benefit from and contribute to PAR in complex decision making contexts. This kind of mutual benefit will be illustrated through a study reported in the area of R&D planning. It will be shown that PAR “contextualizes” problem structuring whereas MS/OR “optimizes” the consensual decision-making process in a multi-organizational context.
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An actor-network theory (ANT) approach: analysis of Turkish e-government gateway initiative
(2009) Aykaç, Didem Selcen Öztürkcan; Kervenoael, R. de; Kasap, N.; Eryarsoy, E.; Business Administration; ÖZTÜRKCAN AYKAÇ, Didem Selcen
There are various models proposed in the literature to analyze trajectories of e-Government projects in terms of success and failure. Yet, only the Actor-Network Theory (ANT) perspective (Heeks and Stanforth, 2007) considers the interaction factors among network actors and actants. This paper proposes the ANT for approaching to the Turkish e-Government Gateway initiative as a case study. In doing so, it provides valuable insight in terms of both local and global actornetworks which surround the initiative.
Open Access
Adaptive pairs trading strategy performance in Turkish derivatives exchange with the companies listed on Istanbul stock exchange
(Springer International Publishing, 2012-03-02) Bolgün, K. E.; Kurun, E.; Güven, Serhat; Güven, Serhat
We implemented model-driven statistical arbitrage strategies in Turkish equities market. Trading signals are generated by optimized parameters of distance method. When the trade in signal is triggered by the model, market-neutral portfolio is created by long in the synthetic ETF, which is based on constrained least squares regression of selected Istanbul Stock Exchange stocks and short in Turkish Derivatives Exchange (Turkdex) index futures contract. We performed pairs trading strategy based on a comparative mean reversion of asset prices with daily data over the period February 2005 through July 2011 in Istanbul Stock Exchange (ISE) and Turkdex. We constructed a hypothetical ISE30 ETF Index on a daily basis in order to originate pairs trading strategy with Turkdex. Because of the leverage rule of (1–10) index futures contracts, we had to evaluate spot stock pairs formation with futures contracts pairs strategy. The results indicate that applied pairs strategy produced overall returns of 901 per cent during the investment period, whereas naive strategy (buy and hold ISE-30 index) return for the same period was 111 per cent. Similar outperformance was observed in the Sharpe and Sortino ratios.
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Addressing endogeneity in the causal relationship between sustainability and financial performance
(Elsevier, 2019-04) Soytaş, Mehmet Ali; Denizel, M.; Uşar, Damla Durak; Economics; SOYTAŞ, Mehmet Ali; Uşar, Damla Durak
The existing empirical literature on the relationship between corporate sustainability performance and corporate financial performance casts doubt on the direction of this relationship although more studies point out a direction from sustainability to performance. Literature also presents a gap in addressing the mechanism(s) of the relationship that hinders the convergence of the empirical findings and only recently the question of causality is being addressed with modern econometric techniques. We argue that due to the potential endogeneity problem in the relationship, an empirical strategy without a theoretical base may result in inconclusive or misleading conclusions. We address the potential endogeneity problem in the relationship and identify the possible causes of this endogeneity as: (i) firm level heterogeneity in financial returns, (ii) the relationship between firm's productivity level and the marginal cost of sustainability initiatives, and (iii) measurement error. We implement Instrumental Variable (IV) technique to overcome these biases. Our results present empirical evidence to support the hypothesis that corporate sustainability is positively related (possibly causally) with corporate financial performance. We further find that sustainability initiatives are more costly for companies that are more productive; thus, they have less incentive to invest. Finally, measurement error in the sustainability metrics does not play a crucial role.
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Algorithmic pairs trading with expert inputs, a fuzzy statistical arbitrage framework
(IOS Press, 2020) Bayram, M.; Akat, Muzaffer; Bulkan, S.; International Finance; AKAT, Muzaffer
Pairs trading is a widespread market-neutral trading strategy aiming to utilize the relationship between pairs of financial instruments in efficient markets, where predictability of separate asset movements is theoretically not possible. The implication of trading pairs, following statistical analysis, is to buy the underpriced asset while short selling the overpriced. The predicted price relationship is determined through analysis of historical spread data between the members of the corresponding pair. The investor expects the price difference, in an efficient market, should converge and stocks return to their ‘fair value’, where the positions are closed and profit is realized. The main focus of this study is the contribution of the fuzzy engine to the existing pairs trading strategy. Widespread classical ‘crisp’ technique is chosen, utilized and compared with the developed ‘fuzzy’ model throughout the paper. In order to further improve this contribution, the expert opinions extracted from the Bloomberg database are also integrated into the fuzzy decision-making process. In most studies, transaction costs are simply ignored. As a final robustness check, the transaction costs are also considered. The improvement reached by the developed fuzzy technique is observed to be even more remarkable in this case.
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Aligning sustainable development principles and sectoral education
(Springer, 2018) Özuyar, Pınar Gökçin; Beyhan, Tugce Baykent; Entrepreneurship; ÖZUYAR, Pinar; Beyhan, Tugce Baykent
The competitive environment for new graduates to acquire a well-paid and satisfying job position and the long-standing gap between recent university graduates and business requirements as to the skills of these graduates, lead to the creation of a Sectoral Education Program model, involving seven different courses with various learning methods ranging from guest speakers, industry analyses and case studies to company practicum projects. The Sectoral Education Program model is a mandatory part of the curriculum for business students and electives for all other students university wide. Emphasized by the launch of sustainable development goals and trying to find complementary and comprehensive examples of innovative tools for private sector–university partnerships, this continuously developing model accepted one of the foci of the program as sustainable development and devised solutions that embed the teaching of sustainable development principles aligning them with concerns of business. In the embedded approach, the curriculum regarding local sectoral expertise, the crosscutting issues for all sectors from population dynamics, resource scarcity to climate change and even big data are being discussed. Over the three semesters of teaching local sectoral expertise in the light of crosscutting issues, students’ feedbacks have been recorded. Main results show that for university students the phrase sustainability is being overused but still the connotation to the real-world cannot be established. By embedding sustainable development principles directly aligned with the concerns of business sectors, majority of the students think that this know-how would be a skill for them in their future prospects.
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Alışveri̇ş merkezleri̇ni̇n Türki̇ye’deki̇ mevzuat çerçevesi̇nde değerlendi̇ri̇lmesi̇
(Middle East Technical University Faculty of Architecture, 2017) Ceylan, R.; Özbakır, B. A.; Erol, Işıl; International Finance; EROL, Işıl
Küresel ölçekte alışveriş merkezlerinin tarihsel gelişim süreci incelendiğinde, ticaret alanlarının alışveriş merkezlerine dönüşüm sürecinde ilk adımların Avrupa’da atıldığı bilinmektedir (Birol, 2005; Geç, 2008 ve Kiriş, 2010). Günümüz alışveriş merkezlerinin ilk örnekleri ise Amerika’da görülmüştür. Kısa bir süre içerisinde modern alışveriş merkezlerinin ilk benzerleri Türkiye de dâhil olmak üzere pek çok ülkede inşa edilmiştir. 1950’li yıllarda Türkiye’nin, gelişmiş ülkelerin perakende sektörü düzenlemelerinden önemli ölçüde etkilendiği görülmektedir. Bu durumun bir sonucu olarak Türkiye’de Migros ve Gima gibi perakende zinciri olan büyük markalar açılmış ve bir perakende altyapısı oluşturulmaya çalışılmıştır. Oluşturulan bu perakende altyapısı, Türkiye’de alışveriş merkezlerinin açılmasında bir altyapı görevi görmüştür. 1990’lı yıllara gelindiğinde, liberal ekonomik politikaların benimsenmesiyle birlikte, toplumdaki yaşam tarzları ve istekleri değişmeye başlamıştır. Ekonominin yabancı sermayeye açılmasının bir yansıması olarak tüketicilerin ithal mallara olan ilgisi artmış ve bu ürünlerin bulunduğu alışveriş merkezleri (AVM) talep görmeye başlamıştır. İstanbul’daki Galleria AVM (1988) ve Ankara’daki Atakule AVM (1989), Türkiye’deki alışveriş merkezlerinin ilk örnekleri olarak kabul edilmektedir. Türkiye’de 2008-2009 küresel finans krizi döneminde dahi 70 adet AVM’nin açılması, AVM gelişiminin oldukça hızlı olduğunu göstermektedir. 2014 yılında Türkiye genelinde faaliyet halinde, inşaat halinde ve proje aşamasında olmak üzere toplam 412 adet AVM bulunmaktadır ve bu merkezlerin toplam kiralanabilir alanı 10,8 milyon m2’ye ulaşmıştır (AARREC, 2015). Bu çalışmanın amacı; günümüzde kentsel alanlarda önemli bir yer edinen ve kentsel sistemi doğrudan etkileyen alışveriş merkezlerini ve alışveriş merkezlerinin gelişimini, Türkiye’deki mevcut mevzuat çerçevesinde değerlendirmektir. Bu amaç doğrultusunda, çalışmanın ikinci bölümünde, planlama dinamikleri çerçevesinde ticaret alanları ve AVM’lerin, dünyadaki ve Türkiye’deki tarihsel gelişim süreçleri özetlenmiştir. Üçüncü bölümde ise, ülkemizde AVM’lerin planlanmasına yönelik olan üç farklı kanun ve yedi yönetmelik detaylı olarak incelenmiştir. Araştırmacılar tarafından yapılan bu inceleme sonucunda güncel mevzuatta eksik bulunan boyutlar ele alınmış ve detaylandırılması gerekli olan konular altı ana değişken altında değerlendirilmiştir. Bu değişkenleri; tanımlar, standartlar ve sınıflandırmalar, yer seçimi kararları, ekolojik çevrenin korunması, ulaşım ve otopark altyapısı, planlar arasındaki hiyerarşi ve lejant içerikleri olarak tanımlamak mümkündür. Çalışmanın dördüncü bölümünde, dünyada ve Türkiye’de alışveriş merkezlerine yönelik politika ve mevzuatın gelişimi ülke örnekleri üzerinden tartışılarak, farklılıklar ve benzerlikler üzerine bir karşılaştırma yapılmıştır. Çalışmanın sonuç bölümünde ise tüm değerlendirme sonuçları özetlenmiş ve mevzuat içerisinde ele alınmayan diğer önemli konulara dikkat çekilmeye çalışılmıştır.
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Altering the environment to improve appointment system performance
(Informs, 2019-06) Çayırlı, Tuğba; Yang, K. K.; Business Administration; ÇAYIRLI, Tuğba
Current research on clinic performance is focused primarily on appointment scheduling rather than shaping the clinical environments. The goal of this study is to investigate the impact of environmental factors on the total cost performance of a clinic, measured as a weighted sum of patients' wait times and physician's idle time and overtime. The environmental factors investigated include the variability of service times, the probabilities of no-shows and walk-ins, the number of appointments per session, and the cost ratio of physician's time to patients' time. The effects of these factors are evaluated using a near-optimal rule that already adjusts the patients' appointment times to minimize the negative effects of these factors so that their residual or true effects on total cost performance can be isolated. As a result, this study provides useful insights for healthcare practitioners in prioritizing their efforts in managing the different sources of variability to further improve the clinic performance beyond the use of an optimal or near-optimal appointment rule. Additional experiments are conducted on the effects of patient and physician unpunctuality, which have been studied to a lesser extent in prior literature.
Open Access
Ambulance location for maximum survival
(Wiley, 2008-02) Erkut, Erhan; Ingolfsson, A.; Erdoğan, G.; Business Administration; ERKUT, Erhan
This article proposes new location models for emergency medical service stations. The models are generated by incorporating a survival function into existing covering models. A survival function is a monotonically decreasing function of the response time of an emergency medical service (EMS) vehicle to a patient that returns the probability of survival for the patient. The survival function allows for the calculation of tangible outcome measures—the expected number of survivors in case of cardiac arrests. The survival-maximizing location models are better suited for EMS location than the covering models which do not adequately differentiate between consequences of different response times. We demonstrate empirically the superiority of the survival-maximizing models using data from the Edmonton EMS system.
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Analysis of cross-country variations in the depth of European mortgage markets
(Springer Science+Business Media, 2016-09) Kutlukaya, M.; Erol, Işıl; International Finance; EROL, Işıl
To date, quantitative analysis on the depth of mortgage markets across a broad set of countries has been very limited. This paper uses a rich and balanced data set on 31 European countries to investigate the cross-country variations in the depth of mortgage markets during the period 2005–2012. The present paper might be accepted as the updated and enriched version of existing research for the European region in terms of the coverage of countries, historical data and the empirical analyses. Our empirical findings reveal that developed countries have sizeable residential mortgage markets and this is mainly associated with higher urbanization rates and stronger legal rights. One of the most notable results of this study is that, statistical significance of explanatory variables in modeling the depth of the mortgage markets depends heavily on both the variables, countries (regions) included in the models and the regression methodology used. Hence, we argue that strong conclusions based on such analyses should be avoided and the findings of previous research on the variations of the depth of mortgage markets should be carefully evaluated.
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Analysis of customer switching behavior in omni-channel retailing
(Institute of Industrial and Systems Engineers, IISE, 2020) Cesaret, Bahriye; Bayram, A.; Business Administration; CESARET, Bahriye
Omni-channel retailing is a recent approach that allows customers to purchase products from anywhere and return them anywhere and allows retailers to fulfill orders from anywhere. This flexibility improves the customer experience by integrating all channels, allows retailers to achieve more availability and drives the sales and traffic of the retailers. In this study, we consider two omni-channel implementations: (i) ship-from-store, and (ii) home delivery, by considering customer switching behavior across the sales channels. Store customers can be fulfilled in store or they can ask for home delivery. Online orders, on the other hand, can be shipped either from the fulfillment center or from any other store location that maximizes the overall profit of the retailer. We further consider that both store and online customers can switch across channels. We build a dynamic programming framework to investigate optimal fulfillment decisions for both online and store orders. We incorporate the uncertainty both in demand and in the cost of shipment to individual customers. We present our results through optimal fulfillment strategies and numerical experiments.
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Anticipating the financial crisis: evidence from insider trading in banks
(Oxford University Press, 2020-04) Akın, Özlem; Marín, J. M.; Peydro, J. - L.; International Finance; PARLAYAN, Özlem Akın
Banking crises are recurrent phenomena, often induced by excessive bank risk-taking, which may be due to behavioural reasons (over-optimistic banks neglecting risks) and to conflicts of interest between bank shareholders/managers and debtholders/taxpayers (banks exploiting moral hazard). We test whether US banks' stock returns in the 2007-8 financial crisis are associated with bank insiders' sales of their own bank's shares in the period prior to 2006Q2 (the peak and reversal in real estate prices). We find that top-five executives' sales of shares predict bank performance during the crisis. Interestingly, effects are insignificant the sales of independent directors and other officers. Moreover, the top-five executives' impact is stronger for banks with higher exposure to the real estate bubble, where a one standard deviation increase of insider sales is associated with a 13.33 percentage point drop in stock returns during the crisis period. Finally, even though bankers in riskier banks sold more shares (furthering their own interests), they did not change their bank's policies, for example, by reducing bank-level exposure to real estate. The informational content of bank insider trading before the crisis suggests that insiders knew that their banks were taking excessive risks, which has important implications for theory, public policy and the understanding of crises, as well as a supervisory tool for early warning signals.
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App popularity: Where in the world are consumers most sensitive to price and user ratings?
(American Marketing Association, 2018-09) Kubler, Raoul Volker; Pauwels, K. H.; Yıldırım, G.; Fandrich, T.; Business Administration; KÜBLER, Raoul Volker
Many companies compete globally in a world in which user ratings and price are important drivers of performance but whose importance may differ by country. This study builds on the cultural, economic, and structural differences across countries to examine how app popularity reacts to price and ratings, controlling for product characteristics. Estimated across 60 countries, a dynamic panel model with product-specific effects reveals that price sensitivity is higher in countries with higher masculinity and uncertainty avoidance. Ratings valence sensitivity is higher in countries with higher individualism and uncertainty avoidance, while ratings volume sensitivity is higher in countries with higher power distance and uncertainty avoidance and those that are richer and have more income equality. For managers, the authors visualize country groups and calculate how much price should decrease to compensate for a negative review or lack of reviews. For researchers, they highlight the moderators of the volume and valence effects of online ratings, which are becoming ubiquitous in this connected world.
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The appreciative democratic voice of DEA: a case of faculty academic performance evaluation
(Elsevier, 2014-03) Oral, Muhittin; Oukil, A.; Malouin, J.-L.; Kettani, O.; Business Administration; ORAL, Muhittin
Data envelopment analysis (DEA) is in fact more than just being an instrument for measuring the relative efficiencies of a group of decision making units (DMU). DEA models are also means of expressing appreciative democratic voices of DMUs. This paper proposes a methodology for allocating premium points to a group of professors using three models sequentially: (1) a DEA model for appreciative academic self-evaluation, (2) a DEA model for appreciative academic cross-evaluation, and (3) a Non-DEA model for academic rating of professors for the purpose of premium allocations. The premium results, called DEA results, are then compared with the premium points “nurtured” by the Dean, called N bonus points. After comparing DEA results and N bonus points, the Dean reassessed his initial bonus points and provided new ones – called DEA-N decisions. The experience indicates that judgmental decisions (Dean's evaluations) can be enhanced by making use of formal models (DEA and Non-DEA models). Moreover, the appreciative and democratic voices of professors are virtually embedded in the DEA models.
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Approximating vehicle dispatch probabilities for emergency service systems with location-specific service times and multiple units per location
(Informs, 2009-02) Budge, S.; Ingolfsson, A.; Erkut, Erhan; Business Administration; ERKUT, Erhan
To calculate many of the important performance measures for an emergency response system, one requires knowledge of the probability that a particular server will respond to an incoming call at a particular location. Estimating these "dispatch probabilities" is complicated by four important characteristics of emergency service systems. We discuss these characteristics and extend previous approximation methods for calculating dispatch probabilities to account for the possibilities of workload variation by station, multiple vehicles per station, call- and station-dependent service times, and server cooperation and dependence.
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An approximation of stochastic hyperbolic equations: case with Wiener process
(Wiley, 2013-06) Ashyralyev, A.; Akat, Muzaffer; International Finance; AKAT, Muzaffer
In the present paper, the two-step difference scheme for the Cauchy problem for the stochastic hyperbolic equation is presented. The convergence estimate for the solution of the difference scheme is established. In applications, the convergence estimates for the solution of difference schemes for the numerical solution of four problems for hyperbolic equations are obtained. The theoretical statements for the solution of this difference scheme are supported by the results of the numerical experiment.

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