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Article Health Capital and a Sustainable Economic-Growth Nexus: a High-Frequency Analysis During Covid-19(Mdpi, 2024) Sungur, Nazli Ceylan; Akdogan, Ece C.; Gokten, SonerThe recent COVID-19 pandemic effectively concretized the vitality of health expenditure and the economic-growth nexus, and the threat of new pandemics make re-examining this relationship a necessity. Consequently, this paper focuses on this nexus for developed OECD countries, paying particular attention to the effects of the COVID-19 pandemic. The use of stock indices as proxy variables for health expenditure and economic growth enabled the examination of this nexus by using high-frequency data and financial econometric techniques, specifically via rolling correlation and bivariate GARCH analyses. The data span 1170 observations between 15 May 2018 and 11 November 2022. Since the research period overlaps with the outbreak of Ukraine-Russia war, additional insights are obtained regarding the effects of the war as well. It was found that an increase in health expenditure leads to a delayed increase in economic growth even in the short term, and this relationship mainly develops during crises such as epidemics, wars, supply chain breakdowns, etc., for developed OECD countries. Given the aging population of developed countries, which will probably deteriorate the health status of those countries in the near future, the increasing political tensions around the globe and the considerations of a global recession highlight the importance and the inevitability of investments in health capital for developed countries as well.Article Nonlinearity and Structural Breaks in Oil Prices: Policy Implications and Macroeconomic Interactions(Walter de Gruyter GmbH, 2026) Omay, Tolga; Sungur, Nazli CeylanThis study examines Brent crude oil price dynamics using an integrated framework of bootstrap sequential break detection and Asymmetric Exponential Smooth Transition Autoregressive (AESTAR) modeling. We demonstrate that oil prices follow an AESTAR process where structural breaks emerge endogenously through dual transition functions, reconciling previously competing explanations in the literature. Analysis of monthly data (1985-2023) identifies major structural shifts coinciding with critical economic events, while revealing these breaks emerge automatically through regime-dependent means. Enhanced testing confirms embedded LSTAR-dominant dynamics with ESTAR components, while skeleton analysis validates the dual equilibrium framework with balanced regime distribution. Generalized Impulse Response Function analysis reveals distinct shock transmission patterns: Tier 1 extreme events (delta max > 1.8) exhibit persistent deviations requiring sustained policy intervention, while Tier 2 events demonstrate mean reversion properties suitable for conventional responses. The framework provides observable threshold levels ($53.62, $37.39) enabling real-time policy intervention, supporting regime-contingent monetary policy and strategic petroleum reserve management protocols. This approach offers policymakers actionable tools for managing oil price volatility through empirically validated intervention strategies.
