Browsing by Author "Omay, Tolga"

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Citation Count: 2
Are CO₂ Emissions Stationary After All? New Evidence from Nonlinear Unit Root Tests
(Springer, 2022) Romero-Avila, Diego; Omay, Tolga; Economics
This study applies a large battery of state-of-the-art nonlinear unit root tests to examine the stationarity properties of carbon dioxide emission series for 28 industrialized countries, five BRICS and seven transition economies over a very long horizon, in some cases over more than two and a half centuries. The application of time-dependent and state-dependent nonlinear unit root tests separately provides mixed evidence regarding the time-series properties of CO2 emissions and a high degree of variability across the different tests. However, the use of hybrid nonlinear unit root tests, combining the presence of structural breaks with symmetric or asymmetric ESTAR adjustment, leads to the rejection of the unit root hypothesis in each of the countries under study with at least one of the hybrid tests. This has important climate policy implications.
Citation Count: 0
Asymmetric Effects of Credit Growth on the Current Account Balance: Panel Data Evidence
(Springer Science and Business Media B.V., 2019) Ekinci,M.F.; Omay,T.; Economics
Expanding current account balances (both surpluses and deficits) prior to the global economic crisis dominated academic and policy debates over the past decade. Understanding the role of credit growth on the current account balance has become a priority particularly with the rebalancing experience in the post-crisis period. In this study, we adopt a comprehensive framework by constructing an empirical model that accommodates asymmetric adjustments of current account balance to the changes in the total and household credit growth. We consider the asymmetric effects in two dimensions. When we discriminate between credit expansion and contraction episodes, our results show that credit growth has a stronger negative impact on the current account balance during credit expansion periods. Furthermore, negative effects of total and household credit growth on the current account balance are more pronounced during current account deficit episodes. © 2019, Springer Nature Switzerland AG.
Citation Count: 17
Behavior of foreign investors in the Malaysian stock market in times of crisis: A nonlinear approach
(Elsevier Science Bv, 2019) Omay, Tolga; Iren, Perihan; Economics
This study investigates the response to crisis of foreign investors versus domestic investors in the Malaysian stock market. The econometric-modeling involves a nonlinear approach which allows for investor responses to differ in up and down markets. Specifically, the smooth-transition autoregressive (STAR-STGARCH) family of models and generalized impulse response function (GIRF) analysis are employed. The 1997 Asian Crisis is analyzed using daily data for the period 1995-2003, and the 2008 Global Financial Crisis for a period extended to 2015 with allowance for structural breaks. The results indicate that foreign investors exhibited herding behavior during the Asian Crisis and responded to the shock more quickly than domestic investors, but that foreigners did not act differently from their domestic counterparts during the Global Financial Crisis. These findings suggest that even as foreign capital flows may be desirable for economic growth, they can be unstable and may increase volatility during crises that are locally rooted. (C) 2018 Elsevier Inc. All rights reserved.
Citation Count: 0
Can governments sleep more soundly when holding international reserves? A banking and financial vulnerabilities perspective*
(Routledge Journals, Taylor & Francis Ltd, 2024) Sallenave, Audrey; Allegret, Jean-Pierre; Omay, Tolga; Economics
We use a sample of 40 developing and emerging countries over the period 1995-2015 to assess the effectiveness of international reserve holding as a crisis mitigator. We test the relevance of the reserve accumulation decreasing returns assumption by estimating the most recent version of the PSTR model. We find that increasing stocks of international reserves allows domestic authorities to mitigate the negative impacts of financial and banking vulnerabilities on GDP growth rates leading to reject the decreasing returns assumption. This evidence is robust to sensitivity checks.
Citation Count: 10
Comparison of optimization algorithms for selecting the fractional frequency in Fourier form unit root tests
(Routledge Journals, Taylor & Francis Ltd, 2021) Omay, Tolga; Emirmahmutoglu, Furkan; Hussain Shahzad, Syed Jawad; Economics
We compare the performance of unit root tests which include flexible Fourier trends in their testing processes. The algorithms considered are those of Broyden, Fletcher, Goldfarb and Shanno (BFGS), Berndt, Hall, Hall and Hausman (BHHH), Simplex, Genetic and grid search (GS). The simulation results indicate that derivative-free methods, such as Genetic and Simplex, have advantages over hill-climbing methods, such as BFGS and BHHH in providing accurate fractional frequencies for fractional frequency flexible Fourier form (FFFFF) unit root test. When the parameters are estimated under the alternative hypothesis of the FFFFF type of unit root test, the grid search and derivative-free methods provide unbiased and efficient estimations. We also provide the asymptotic distribution of the FFFFF unit root test. We extend the FFFFF unit root test to a panel version in order to increase the power of the test. Finally, the empirical analyses of healthcare convergence show that derivative-free methods, hill climbing and extensive grid searches can be used interchangeably. However, for big data and accurate estimation of the frequency parameters, the Simplex methodology using the bootstrap process is preferred.
Citation Count: 0
Comparison of the Performance of Structural Break Tests in Stationary and Nonstationary Series: A New Bootstrap Algorithm
(Springer, 2024) Camalan, Ozge; Hasdemir, Esra; Omay, Tolga; Kucuker, Mustafa Can; Economics; International Trade and Logistics
Structural breaks are considered as permanent changes in the series mainly because of shocks, policy changes, and global crises. Hence, making estimations by ignoring the presence of structural breaks may cause the biased parameter value. In this context, it is vital to identify the presence of the structural breaks and the break dates in the series to prevent misleading results. Accordingly, the first aim of this study is to compare the performance of unit root with structural break tests allowing a single break and multiple structural breaks. For this purpose, firstly, a Monte Carlo simulation study has been conducted through using a generated homoscedastic and stationary series in different sample sizes to evaluate the performances of these tests. As a result of the simulation study, Zivot and Andrews (J Bus Econ Stat 20(1):25-44, 1992) are the best-performing tests in capturing a single break. The most powerful tests for the multiple break setting are those developed by Kapetanios (J Time Ser Anal 26(1):123-133, 2005) and Perron (Palgrave Handb Econom 1:278-352, 2006). A new Bootstrap algorithm has been proposed along with the study's primary aim. This newly proposed Bootstrap algorithm calculates the optimal number of statistically significant structural breaks under more general assumptions. Therefore, it guarantees finding an accurate number of optimal breaks in real-world data. In the empirical part, structural breaks in the real interest rate data of the US and Australia resulting from policy changes have been examined. The results concluded that the bootstrap sequential break test is the best-performing approach due to the general assumption made to cover real-world data.
Citation Count: 1
Controlling Heterogeneous Structure of Smooth Breaks in Panel Unit Root and Cointegration Testing
(Springer, 2023) Omay, Tolga; Iren, Perihan; Economics
This study aims to show the consequences of a restrictive homogeneity assumption of frequency in heterogeneous panel unit root and cointegration testing with Flexible Fourier Form. For this purpose, we use a simple panel unit root and residual based cointegration test with Flexible Fourier Form in a heterogeneous frequency setting using a bootstrap algorithm. The power of the test statistics and empirical analysis results indicate that failing to take into account a heterogeneous frequency may lead to misleading inferences, thereby leading to misspecified tests and erroneous conclusions concerning the stochastic behavior of the data in the panel sample.
Citation Count: 3
Convergence of economic growth and health expenditures in OECD countries: Evidence from non-linear unit root tests
(Frontiers Media Sa, 2023) Celik, Esref Ugur; Omay, Tolga; Tengilimoglu, Dilaver; Business; Economics
IntroductionThe relationship between human capital, health spending, and economic growth is frequently neglected in the literature. However, one of the main determinants of human capital is health expenditures, where human capital is one of the driving forces of growth. Consequently, health expenditures affect growth through this link. MethodsIn the study, these findings have been attempted to be empirically tested. Along this axis, health expenditure per qualified worker was chosen as an indicator of health expenditure, and output per qualified worker was chosen as an indicator of economic growth. The variables were treated with the convergence hypothesis. Due to the non-linear nature of the variables, the convergence hypothesis was carried out with non-linear unit root tests. ResultsThe analysis of 22 OECD countries from 1976 to 2020 showed that health expenditure converged for all countries, and there was a significant degree of growth convergence (except for two countries). These findings show that health expenditure convergence has significantly contributed to growth convergence. DiscussionPolicymakers should consider the inclusiveness and effectiveness of health policies while making their economic policies, as health expenditure convergence can significantly impact growth convergence. Further research is needed to understand the mechanisms behind this relationship and identify specific health policies most effective in promoting economic growth.
Citation Count: 1
Convergence of GHGs emissions in the long-run: aerosol precursors, reactive gases and aerosols-a nonlinear panel approach
(Springer, 2023) Romero-Avila, Diego; Omay, Tolga; Economics
Anthropogenic emissions of reactive gases, aerosols and aerosol precursor compounds are responsible for the ozone hole, global warming and climate change, which have altered ecosystems and worsened human health. Environmental authorities worldwide have responded to these climate challenges through the 2030 Agenda for Sustainable Development. In this context, it is key to ascertain empirically whether emission levels are converging among the countries forming the industrialized world. In doing so, we focus on 23 industrialized countries using a novel dataset with ten series of annual estimates of anthropogenic emissions that include aerosols, aerosol precursor and reactive compounds, and carbon dioxide over the 1820-2018 period. We apply four state-of-the-art panel unit root tests that allow for several forms of time-dependent and state-dependent nonlinearity. Our evidence supports stochastic convergence following a linear process for carbon dioxide, whereas the adjustment is nonlinear for black carbon, carbon monoxide, methane, non-methane volatile organic compounds, nitrous oxide, nitrogen oxides and sulfur dioxide. In contrast, ammonia and organic carbon emissions appear to diverge. As for deterministic convergence, carbon dioxide converges linearly, while black carbon, carbon monoxide, nitrogen oxides, non-methane volatile organic compounds and sulfur dioxide adjust nonlinearly. Our results carry important policy implications concerning the achievement of SDG13 of the global 2030 Agenda for Sustainable Development, which appears to be feasible for the converging compounds.
Citation Count: 8
Convergence of per capita energy consumption around the world: New evidence from nonlinear panel unit root tests
(Elsevier, 2022) Romero-Avila, Diego; Omay, Tolga; Economics
This paper investigates the existence of stochastic and deterministic convergence in per capita energy consumption among the countries forming four income-level groups and a full sample of 110 countries over the 1971-2019 period. For that purpose, we employ six state-of-the-art nonlinear panel unit root tests with nonlinear dynamics that range from state-dependent nonlinearities such as ESTAR, AESTAR and TAR dynamics to timedependent nonlinearities of structural break form. We find consistent evidence supporting stochastic convergence among high-income and upper-middle-income countries according to two of the six panel tests. Concerning the stronger notion of deterministic convergence, three tests point to deterministic convergence among high-income countries, and only one supports this hypothesis among upper-middle-income countries. Lack of convergence across all country groups carries important policy implications concerning the achievement of SDG7 of the global 2030 Agenda for Sustainable Development that affects every single country in the planet.
Citation Count: 7
Current account and credit growth: The role of household credit and financial depth
(Elsevier Science inc, 2020) Ekinci, Mehmet Fatih; Omay, Tolga; Economics
Understanding the impact of financial variables on the current account balance is one of the priorities of academic literature and policymakers. Evidence from a broad panel of advanced and emerging countries shows that an increase in credit growth is associated with a significant deterioration in the current account balance. When we examine the roles of the components of credit, we find that an increase in household credit causes a significant decline in the current account balance, whereas an increase in business loans has no significant effect. Therefore, our findings indicate that the significant negative impact of credit growth on the current account balance is driven by household credit. Furthermore, we show that total and household credit growth rates have a stronger negative effect on the current account balance for lower levels of financial depth. Our results suggest that targeted policy measures that curb household credit growth might be more effective to reduce external imbalances particularly at the early stages of financial deepening.
Citation Count: 4
Does real UK GDP have a unit root? Evidence from a multi-century perspective
(Routledge Journals, Taylor & Francis Ltd, 2020) Canarella, Giorgio; Gupta, Rangan; Millera, Stephen M.; Omay, Tolga; Economics
We employ linear and nonlinear unit-root tests to examine the stationarity of five multi-century historical U.K. series of real output compiled by the Bank of England. Three series span 1270 to 2016 and two series span 1700 to 2016. These datasets represent the longest span of historical real output data available and, thus, provide the environment for which unit-root tests are most powerful. A key feature of our test is its simultaneous allowance for two types of nonlinearity: time-dependent (structural breaks) nonlinearity and state-dependent (asymmetric adjustment) nonlinearity. The key finding of the test, contrary to what other more popular nonlinear unit-root tests suggest, provides strong evidence that the main structure of the five series is a stationary process characterized by an asymmetric nonlinear adjustment and a permanent break affecting both the intercept and the trend. A major policy implication of this finding is fiscal and/or monetary stabilization policies have only temporary effects on the output levels of the United Kingdom.
Citation Count: 2
The effects of energy-intensive meat production on CO₂ emissions: evidence from extended environmental Kuznets framework
(Springer Heidelberg, 2022) Bor, Ozgur; Omay, Tolga; Iren, Perihan; Aktan, Ceyda; Economics
This study documents the positive relationship between meat production and CO2 emissions by utilizing the environmental Kuznets framework. Relationships between energy consumption, economic growth, meat production, and the levels of CO2 are tested using 6 different variables (CO2 emissions, GDP, energy consumption, forest area, total meat, and total livestock). Data for the study is related to the G7 countries and covers the period between 1961 and 2016. The analysis of the data is then conducted using a panel threshold model. Moreover, the extended EKC model does not only consider the income as the state variable but also examines the nonlinear structure inherited in other explanatory variables as a state variable. In this way, we have seen the nonlinear effects of other variables' evolution over time on carbon emission. The overall results indicate that the production of meat significantly increases CO2 emissions.
Citation Count: 11
Environmental Kuznets Curve: Non-Linear Panel Regression Analysis
(Springer, 2020) Senturk, Huseyin; Omay, Tolga; Yildirim, Julide; Kose, Nezir; Economics
This study presents an analysis of the relationship between per capita CO2 emissions as an environmental degradation indicator and per capita gross domestic product (GDP) as an economic growth indicator within the framework of the Environmental Kuznets Curve (EKC). For this purpose, non-linear panel models are estimated for the Annex I countries, non-Annex countries, and whole parties with respect to data availability of the United States Convention on Climate Change (UNFCCC) for the period 1960-2012. The empirical results of the panel smooth transition models (PSTR) show that the environmental deterioration rises in the first phase of growth for all data sets. Afterwards, the environmental degradation cannot be prevented, but the increase in the amount of environmental degradation decreases. The findings of this study give an insight regarding the differential environmental impact of economic growth between developed and developing countries. While the validity of a traditional EKC relation regarding the CO2 emissions cannot be affirmed for any group of countries in our sample, empirical results indicate the existence of multiple regimes where economic growth hampers environmental quality, but its severity decreases at each consecutive regime.
Citation Count: 2
Examining the non-linear stochastic behavior of the European energy market: evidence from nonlinear unit root tests
(Taylor & Francis inc, 2022) Aktan, Ceyda; Omay, Tolga; Sahin, Eyyup Ensari; Economics
Stock market efficiency has been one of the most investigated topics of the last century. Knowing the efficiency of a market has major implications for both investors and policymakers, as a perfectly efficient market eliminates any arbitrage opportunity and the possibility of actually beating the market. For this reason, this study aims to examine the weak-form market efficiency of the European energy markets using linear and nonlinear unit root tests for the period covering February 2012 to April 2021. The results indicated that while the Augmented Dickey-Fuller test captured the stationarity in only Austria's Oil, and Gas index, using nonlinear tests showed stationarity in 17 of the 20 indices tested. Overall, the European Energy Market can be considered inefficient under the weak form of the Efficient Market Hypothesis. Therefore, there is an indication of profitable arbitrage opportunities among energy stocks. Signs of stationarity also suggest that shocks to energy stocks will have temporary effects. Energy markets of Austria, Finland, France, Greece, Italy, Netherlands, Russia, Spain, Sweden, and the United Kingdom, for this reason, could benefit from policy changes to support increased information flow to achieve more transparency and utilize better trading technologies.
Citation Count: 1
Fiscal Sustainability from a Nonlinear Framework: Evidence from 14 European Countries
(Springer Science and Business Media B.V., 2019) Hasdemir,E.; Omay,T.; Department of Basic English (Prep School); International Trade and Logistics; Economics
This study examines the fiscal sustainability of 14 European Union (EU) Member countries in the long run. For this purpose, a linear Augmented Dickey Fuller (ADF) and a variety of nonlinear univariate unit root tests are applied to the debt-to-GDP series of the 14 EU Member countries; Belgium, Czech Republic, Denmark, Finland, France, Greece, Hungary, Italy, Netherlands, Poland, Portugal, Romania, Slovakia and Sweden. In addition to that, the nonlinear unit root tests applied in this study are classified according to the source of nonlinearities: (i) time dependent nonlinearity (structural break(s)), (ii) state dependent nonlinearity and (iii) hybrid nonlinearity. Thus, the nonlinearities and their sources in data generating process of debt-to-GDP series of every country can be determined. The findings of this study show that the null of linear unit root cannot be rejected for none of the countries by applying linear ADF whereas it can be rejected as a result of nonlinear unit root tests for considerable number of countries, i.e. 11 out of 14 countries exhibit time dependent nonlinearity, 6 out of 14 exhibit state dependent nonlinearity and 10 out of 14 exhibit hybrid nonlinearity in their relevant data. So, the source of nonlinearities in the relevant data differs according to the country. That is, for testing the fiscal sustainability, the nonlinearities in the data need to be taken into account. Ignoring the nonlinearities in the testing procedure can lead misleading results in the decision of fiscal sustainability in the long run. © 2019, Springer Nature Switzerland AG.
Citation Count: 24
Fractional unit-root tests allowing for a fractional frequency flexible Fourier form trend: predictability of Covid-19
(Springer, 2021) Omay, Tolga; Baleanu, Dumitru; Economics
In this study we propose a fractional frequency flexible Fourier form fractionally integrated ADF unit-root test, which combines the fractional integration and nonlinear trend as a form of the Fourier function. We provide the asymptotics of the newly proposed test and investigate its small-sample properties. Moreover, we show the best estimators for both fractional frequency and fractional difference operator for our newly proposed test. Finally, an empirical study demonstrates that not considering the structural break and fractional integration simultaneously in the testing process may lead to misleading results about the stochastic behavior of the Covid-19 pandemic.
Citation Count: 35
Global risk aversion and emerging market return comovements
(Elsevier Science Sa, 2018) Demirer, Riza; Omay, Tolga; Yuksel, Asli; Yuksel, Aydin; Economics
Utilizing the recently developed measure of global risk aversion by Xu (2017), we show that global risk aversion is a significant determinant of international equity correlations, consistently across all emerging markets examined. The positive effect of risk aversion on emerging market comovements is particularly strong for South Africa and Turkey and is consistent with contagion effects. The results underscore the importance of non-cash flow shocks in models of contagion and portfolio risk. (C) 2018 Elsevier B.V. All rights reserved.
Citation Count: 2
High Persistence and Nonlinear Behavior in Financial Variables: A More Powerful Unit Root Testing in the ESTAR Framework
(Mdpi, 2021) Omay, Tolga; Corakci, Aysegul; Hasdemir, Esra; Economics; International Trade and Logistics
In this study, we consider the hybrid nonlinear features of the Exponential Smooth Transition Autoregressive-Fractional Fourier Function (ESTAR-FFF) form unit root test. As is well known, when developing a unit root test for the ESTAR model, linearization is performed by the Taylor approximation, and thereby the nuisance parameter problem is eliminated. Although this linearization process leads to a certain amount of information loss in the unit root testing equation, it also causes the resulting test to be more accessible and consistent. The method that we propose here contributes to the literature in three important ways. First, it reduces the information loss that arises due to the Taylor expansion. Second, the research to date has tended to misinterpret the Fourier function used with the Kapetanios, Shin and Snell (2003) (KSS) unit root test and considers it to capture multiple smooth transition structural breaks. The simulation studies that we carry out in this study clearly show that the Fourier function only restores the Taylor residuals of the ESTAR type function rather than accounting forthe smooth structural break. Third, the new nonlinear unit root test developed in this paper has very strong power in the highly persistent near unit root environment that the financial data exhibit. The application of the Kapetanios Shin Snell- Fractional Fourier (KSS-FF) test to ex-post real interest rates data of 11 OECD countries for country-specific sample periods shows that the new test catches nonlinear stationarity in many more countries than the KSS test itself.
Citation Count: 0
Hisse Senedi Getirileri, Bitcoin Getirileri ve Riskten Kaçınma Arasındaki İlişki: Çok Değişkenli Bir GARCH Modelinden Kanıtlar
(Sosyoekonomi Soc, 2021) Sivrikaya, Ayşen; İren, Perihan; Omay, Tolga; Economics
Bu çalışma, çok değişkenli bir GARCH modeli kullanarak ABD Dow Jones Borsasında işlem gören hisse senedi getirileri, Bitcoin getirileri ve bunların belirsizlikleri arasındaki ilişkileri araştırmaktadır. Özellikle, yüksek ve düşük olmak üzere farklı risk iştahının ve getirilerde belirsizliğin yüksek olduğu dönemlerde Bitcoin ve ABD hisse senedi getirilerinin verdiği tepkileri karşılaştırmaktadır. Sonuçlar, Bitcoin getirisinin riskten kaçınılan veya yüksek belirsizliğin olduğu dönemlerde hisse senedi gibi tepki verdiğini, ancak iki getiri arasındaki ilişkinin sürdürülebilir olmadığını göstermektedir. Öte yandan, ABD borsa yatırımcıları tüm örneklem dönemi boyunca riskten kaçınma davranışını gösterirken, Bitcoin yatırımcıları aynı davranışı göstermemektedir.