Ekonometride Güncel Yöntemler ve Uygulamalar
GARCH, Yapay Sinir Ağları ve Destek Vektör Regresyonu Yöntemlerinin Karşılaştırılması: BİST Hizmetler Endeks Getirisi Örneği
Nimet Melis Esenyel İçenHisse senedi fiyatlarındaki oynaklığın tahmin edilmesi, hem bireysel hem kurumsal düzeyde yatırımcılar için önemini korumaktadır. Bu bakımdan uygun tahmin yönteminin belirlenmesi uzun zamandır araştırmacıların ve yatırımcıların üzerinde durduğu bir konu olmuştur. Çalışmada, klasik oynaklık modelleri ve yapay zeka modelleri kullanılarak Borsa İstanbul hizmetler endeks getirisinin öngörü performansının karşılaştırılması amaçlanmıştır. Klasik ve yapay zeka modellerine ek olarak hibrit modeller de oluşturulmuştur ve hibrit modellerin öngörü performansını arttırıp arttırmadığı incelenmiştir. Analize konu olan hizmetler sektörünün önemi, gelişmiş ve gelişmekte olan ülkelerde tarım ve sanayi sektörlerine kıyasla daha fazla gelişme göstermesidir. Bunun yanı sıra hizmet sektörü sektörel bazda yüksek bir paya sahip olduğundan ülkelerin gelişmişlik düzeyi ile alakalı olarak görülmektedir. Dolayısıyla hizmetler endeksinin modellenmesi ve tahmini önemli olmaktadır. Analizde kullanılan Borsa İstanbul hizmetler endeksi verileri TCMB Elektronik Veri Dağıtım Sisteminden alınmış olup, 05.01.2009- 13.11.2020 dönemini kapsayan günlük frekanstadır. Analiz sonucuna göre oluşturulan on model içerisinde öngörü performansı en yüksek modellerin hibrit modellerden DVR-EGARCH ve ELM-EGARCH olduğu görülmüştür.
Comparison of Garch, Artificial Neural Networks, and Support Vector Regression Methods: the Case of the BIST Services Index Return
Nimet Melis Esenyel İçenMeasuring the volatility in stock prices is an important research concern at both individual and institutional levels. Individuals and businesses want to know the fluctuation of prices to avoid portfolio losses and to make profitable investments. Countries also try to understand the volatility in stock prices to determine investment policies at the international level. Consequently, establishing the appropriate estimation method has long been a topic of focus for researchers and investors alike.
Methods used in forecasting stock returns are generally classified as linear and nonlinear models. Linear models include autoregressive integrated moving average, exponential smoothing, and generalized autoregressive conditional heteroskedasticity (GARCH), among others. These models are mainly based on an assumption of linearity between variables that are normally distributed. Most of the studies that attempt to reveal the relationship between stock returns and financial and economic variables are based on simple linear regression assumptions. However, no evidence supports the assumption that this relationship is entirely linear. The significance of residual variance and the ability to explain this residual variance with nonlinear models makes it possible to obtain more reliable predictions using nonlinear models. Nonlinear models include those based on artificial intelligence, such as artificial neural networks (ANN), support vector machines, genetic algorithms, and particle swarm optimization. The assumption of linearity and normality may not be provided in the modeling of stock price movements. For this reason, artificial intelligence methods that have no restrictive assumptions have been recommended in the literature. These methods can also identify nonlinear structures, and have been shown to perform better empirically than statistical methods.
This study aims to compare the forecasting performance of the Borsa Istanbul (BIST) services index return applying classical volatility and artificial intelligence models. In addition to these models, hybrid models were also created to investigate whether hybrid models increase forecasting performance. The GARCH and exponential generalized autoregressive conditional heteroskedasticity (EGARCH), which are linear volatility models, as well as ANN and support vector regression (SVR), which are nonlinear models, will be used to predict stock returns. Hybrid models will also be created by combining ANN and SVR with GARCH and EGARCH models.
The services index is the stock market index calculated by considering changes in the stock prices of only services sector companies traded in the national market. There are 65 companies traded in the BIST services sector, and approximately 38% of these companies are in the “wholesale and retail trade, restaurants, and hotels” sector. The importance of the services sector is that it is more established in both developed and developing countries, as opposed to agricultural and industrial sectors. In addition, as the service sector has a high share on a sectoral basis, it is seen as related to a country’s development level, making the modeling and forecasting of the BIST services index an important consideration. The daily data used in the analysis is obtained from the Central Bank Electronic Data Delivery System covering the period 05.01.2009–13.11.2020. The results indicate that among the 10 models created and applied, those with the highest forecasting performance are the hybrid models SVR-EGARCH and extreme learning machine-EGARCH.