Browsing by Author "Zsurkis, Gabriel Florin"
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- Are linear models really unuseful to describe business cycle data?Publication . Lopes, Artur Silva; Zsurkis, Gabriel FlorinWe use first differenced logged quarterly series for the GDP of 29 countries and the euro area to assess the need to use non-linear models to describe business cycle dynamic behaviour. Our approach is model (estimation)-free, based on testing only. We aim to maximize power to detect non-linearities while, simultaneously, avoiding the pitfalls of data mining. The evidence we find does not support some descriptions because the presence of significant non-linearities is observed for two-thirds of the countries only. Linear models cannot be simply dismissed as they are frequently useful. Contrarily to common knowledge, non-linear business cycle variation does not seem to be a universal, undisputable and clearly dominant stylized fact. This finding is particularly surprising for the U.S. case. Some support for non-linear dynamics for some further countries is obtained indirectly, through unit root tests, but this can hardly be invoked to support non-linearity in classical business cycles.
- Assimetrias nos ciclos económicos : modelação não linear do PIB de alguns paísesPublication . Zsurkis, Gabriel Florin; Lopes, Artur SilvaEsta dissertação pretende investigar a existência de não-linearidades nos ciclos económicos de vários países através dos modelos STAR(Smooth Transition AR), à semelhança de Bradley e Jansen(2000). Os vários testes de linearidade realizados fornecem evidência de não-linearidades na taxa de crescimento do PIB para a grande maioria dos países, sendo a evidência contra a hipótese nula de linearidade mais forte que no artigo acima referido.No entanto, tal como nesse trabalho, não foi possível encontrar características comuns nos ciclos económicos dos países estudados.A heterogeneidade revela-se quer na utilização de modelos adequados diferentes quer, para o mesmo modelo, em estimativas bastante diferentes dos parâmetros e dos números de desfasamentos.
- Essays on Econometrics : Nonlinearities and NonnormalitiesPublication . Zsurkis, Gabriel Florin; Nicolau, João; Rodrigues, PauloThis Dissertation consists of three independent papers on econometrics, having in common the fact that each of them proposes a new methodology to deal with issues caused by the departure from linearity and gaussianity assumptions. We start by introducing a simple and easy to implement procedure to test for multiple structural changes in persistence. An in-depth Monte Carlo analysis shows that the new procedure performs well under various DGPs with persistence changes. The application of the proposed test to OECD countries inflation reveals relevant statistical evidence of breaks in persistence for all countries. Overall, the persistence was high and non-mean-reverting until the early 80’s and subsequently decreased, which coincides with the beginning of the Great Moderation. Then, the second paper introduce a flexible framework able to capture some aspects of the potential nonlinear causal relationships between economic variables. More precisely, the proposed procedure estimates the expected time (ET) an outcome variable takes to cross a fixed threshold given a starting value and conditional on covariates. An application to the economic activity-yield spread relationship for the U.S. suggests that the yield spread may have an important role in stimulating a faster return to desirable growth rates when the economy is in contraction or faces weak growth. Moreover, negative yield spread values in the presence of positive and high industrial production growth rates leads to a quick return to negative growth rates and may trigger a recession. Finally, the third paper proposes a simple framework that allows us to take into account the magnitude of potential losses incurred throughout the investment horizon, denoted intra-horizon risk, in portfolio optimization. To this end, we introduce a novel nonparametric method to estimate the first passage probability function that only make use of the Markovian property of the returns. An empirical application is provided considering equity, bond and commodity Exchange Traded funds (ETFs). Our results suggest that the proposed framework indicates portfolios with lower expected time to reach the target return than those indicated by the Markowitz’ mean-variance approach with similar levels of intra-horizon risk, which may result in higher expected annualized return if the lower threshold that triggers a stop-loss decision is not crossed.