İşletme Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/403

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Citation - WoS: 1
Citation - Scopus: 2
A new causal discovery heuristic
(Springer, 2018) Prestwich, S. D.; Özkan, İbrahim; Tarim, S. A.; Ozkan, I.; 6641; 169580; Yönetim Bilişim Sistemleri
Probabilistic methods for causal discovery are based on the detection of patterns of correlation between variables. They are based on statistical theory and have revolutionised the study of causality. However, when correlation itself is unreliable, so are probabilistic methods: unusual data can lead to spurious causal links, while nonmonotonic functional relationships between variables can prevent the detection of causal links. We describe a new heuristic method for inferring causality between two continuous variables, based on randomness and unimodality tests and making few assumptions about the data. We evaluate the method against probabilistic and additive noise algorithms on real and artificial datasets, and show that it performs competitively.
Citation - WoS: 19
Citation - Scopus: 21
An Extended Mixed-Integer Programming Formulation and Dynamic Cut Generation Approach for the Stochastic Lot-Sizing Problem
(informs, 2018) Tunc, Huseyin; Kilic, Onur A.; Tarim, S. Armagan; Rossi, Roberto; 6641
We present an extended mixed-integer programming formulation of the stochastic lot-sizing problem for the static-dynamic uncertainty strategy. The proposed formulation is significantly more time efficient as compared to existing formulations in the literature and it can handle variants of the stochastic lot-sizing problem characterized by penalty costs and service level constraints, as well as backorders and lost sales. Also, besides being capable of working with a predefined piecewise linear approximation of the cost function-as is the case in earlier formulations-it has the functionality of finding an optimal cost solution with an arbitrary level of precision by means of a novel dynamic cut generation approach.
Citation - WoS: 4
Citation - Scopus: 5
Does workplace envy always have detrimental consequences in organizations? A study of public and private sector employees
(Emerald Group Publishing Ltd, 2022) Sener, Irge; Şener, İrge; Karabay, Melisa Erdilek; Elci, Meral; Erman, Halil; 21583; İşletme
Purpose Based on the situational approach for envy, the purpose of this paper is to examine the effect of two-dimensional workplace envy (being envied and envying others) on the task and contextual performance of employees working in either private or public sector organizations. Design/methodology/approach This study was conducted on survey data collected from 988 private sector employees and 530 employees from the public sector employed in Istanbul. Following a quantitative empirical design, structural equation modeling was used to test the hypotheses. Findings The study results revealed that envying-others dimension has a significant negative effect on both task performance and contextual performance. In addition, the findings indicate more envious feelings of private sector employees than public sector employees. For public sector employees, male participants were found to envy others more than females. Research limitations/implications In addition to the contributions, this study has its limitations. First, although the study was carried out with a comprehensive sample, it is limited to the views of 1,518 employees in Istanbul and is a cross-sectional study. Also, employee performance is evaluated through self-reporting, which forms another limitation; it could have been more reliable for the supervisors to assess their subordinates' performance. Practical implications Apart from scholars, our findings have implications for practitioners. Feelings such as envy that comes with a sense of competition can create an environment that stimulates people, motivates them to work, can make them productive and can also cause an ultimately destructive situation. This makes it critical to manage envy in the workplace. Though there may be facilitators behind it, one crucial factor that fuels envy in the workplace is the lack of fair human resources policies and systems. Still, human resources management is undeveloped in most public organizations. With effective human resources management, there may be some roadmaps for managers to dissolve conflicts arising from envy. First, it is imperative to have systems that will separate the employee from the others, which everyone will accept, strengthening the feelings of justice among employees. Envy often occurs following a social comparison. Management can implement an incentive system that supports employee collaboration and avoid nepotism. Especially in private organizations where the competition is more among employees, managers should give more attention to understand their subordinates' feelings. The managers' attention to expressing their feelings toward their subordinates could establish an equal distance within the workplace. In this sense, language selection is critical, and managers should be mindful of linguistic triggers. Managers should not avoid giving both positive and negative feedback to their employees. Unwarranted and unsystematic reward and/or punishment systems, made with the good intentions of increasing competition, can trigger envy. Finally, managers should implement an open-door policy and open communication that will encourage all team members to be transparent to each other. Originality/value The study was based on a rationale that envy has detrimental workplace outcomes that lead to low task and contextual performance. Although there exists a recent interest for examining the relation between workplace envy and employee performance, based on being envied and envying others dimensions, these studies are limited. This study focuses on these dimensions and performance relations, and it also provides a comparative outlook for public and private sector employees in Turkey in terms of workplace envy.
Citation - WoS: 4
Citation - Scopus: 3
Fixed Point Results Via Simulation Functions in the Context of Quasi-Metric Space
(Univ Nis, Fac Sci Math, 2018) Fulga, Andreea; Tas, Aysegul; 29252
In this paper, we investigate the existing non-unique fixed points of certain mappings, via simulation functions in the context of quasi-metric space. Our main results generalize and unify several existing results on the topic in the literature.
Citation - Scopus: 21
Forecasting stock market volatility: Further international evidence
(2006) Balaban, E.; Bayar, A.; Faff, R.W.
This paper evaluates the out-of-sample forecasting accuracy of eleven models for monthly volatility in fifteen stock markets. Volatility is defined as within-month standard deviation of continuously compounded daily returns on the stock market index of each country for the ten-year period 1988 to 1997. The first half of the sample is retained for the estimation of parameters while the second half is for the forecast period. The following models are employed: a random walk model, a historical mean model, moving average models, weighted moving average models, exponentially weighted moving average models, an exponential smoothing model, a regression model, an ARCH model, a GARCH model, a GJR-GARCH model, and an EGARCH model. First, standard (symmetric) loss functions are used to evaluate the performance of the competing models: mean absolute error, root mean squared error, and mean absolute percentage error. According to all of these standard loss functions, the exponential smoothing model provides superior forecasts of volatility. On the other hand, ARCH-based models generally prove to be the worst forecasting models. Asymmetric loss functions are employed to penalize under-/over-prediction. When under-predictions are penalized more heavily, ARCH-type models provide the best forecasts while the random walk is worst. However, when over-predictions of volatility are penalized more heavily, the exponential smoothing model performs best while the ARCH-type models are now universally found to be inferior forecasters.
Citation - WoS: 9
Citation - Scopus: 15
Stock returns and volatility: empirical evidence from fourteen countries
(Routledge Journals, Taylor & Francis Ltd, 2005) Balaban, E; Bayar, A
This is a pioneering effort to test in 14 countries the relationship between stock market returns and their forecast volatility derived from the symmetric and asymmetric conditional heteroscedasticity models. Both weekly and monthly returns and their volatility are investigated. An out-of-sample testing methodology is employed using volatility forecasts instead of investigating the relation between stock returns and their in-sample volatility estimates. Expected volatility is derived from the ARCH(p), GARCH(1, 1), GJR-GARCH(1, 1) and EGARCH(1, 1) forecast models. Expected volatility is found to have a significant negative or positive effect on country returns in a few cases. Unexpected volatility has a negative effect on weekly stock returns in six to seven countries and on monthly returns in nine to eleven countries depending on the volatility forecasting model. However, it has a positive effect on weekly and monthly returns in none of the countries investigated. It is concluded that the return variance may not be an appropriate measure of risk.
Citation - WoS: 4
Citation - Scopus: 5
Tackling service quality in the telecommunication B2B market
(Emerald Group Publishing Ltd, 2019) Tas, Aysegul; Ergin, Elif Akagun; Kurtulmusoglu, Feride Bahar; Sahin, Omer Faruk; 29252; 120408
Purpose This study will attempt to focus on how vendors serve operators, as operator service quality starts with vendor's technology infrastructure and service quality. The purpose of this study is to exhibit the most important vendor service quality items and dimensions for the operators in the telecommunications industry. Design/methodology/approach A total of 268 employees from various age groups, cities, job levels and departments participated in the survey. Findings Expected service quality results indicated that operators need high service quality. When telecommunication needs of subscribers are taken into account, it is normal for operators to expect high service quality from vendors. Results also reveal that being dependable and providing continuous support are critical for the telecommunications industry. Perceived service quality results demonstrate that customer expectations failed to be satisfied. In this study conducted in the telecommunications market, the expectations of operator employees regarding vendors is shaped under two dimensions. These dimensions are employee and service center features and provider timeliness and accuracy. When Topsis method was used to determine the most important vendor characteristics, timeliness and trust were identified as the top two criteria. Originality/value To the best of the authors' knowledge, this study is the first to put forth the most important vendor service quality items and dimensions for the operators in the telecommunications industry.
Citation - WoS: 11
Citation - Scopus: 15
The mediating role of trust in leader in the relations of ethical leadership and distributive justice on internal whistleblowing: a study on Turkish banking sector
(Emerald Group Publishing Ltd, 2021) Alpkan, Lutfihak; Şener, İrge; Karabay, Melisa; Sener, Irge; Elci, Meral; Yildiz, Bora; 21583; İşletme
Purpose The purpose of this paper is to explain the effect of perceived ethical leadership and perceived distributive justice on internal whistleblowing intention through trust in leader as a mediator. Design/methodology/approach Following an empirical design, data were collected from 1,296 employees of Turkish financial institutions, located in Istanbul. To test four hypotheses structural equation modelling was applied. Findings Results reveal that trust in a leader fully mediates the positive effects of both ethical leadership and distributive justice on the internal whistleblowing intention. Originality/value This study enhances the understanding of the ethical leadership perception and distributive justice affecting the internal whistleblowing intention in Turkey that is a developing country. Although numerous studies on whistleblowing have been conducted, this study's originality and contribution lay in the examination of trust in the leader as a missing link between the direct relations.

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