This paper aims to model the change in market share of 30 domestic and foreign banks, which have been operating between the years 1990 and 2009 in Turkey by taking into consideration 20 financial ratios of those banks. Due to the fragile structure of the banking sector in Turkey, this study plays an important role for determining the changes in market share of banks and taking the necessary measures promptly. For this reason, computational intelligence methods have been used in the study. According to the research results, it is seen that it was not able to properly anticipate the data for the banking sector in the periods of financial crises (2000-2001 and 2008-2009). However, it is seen that, Simple Linear Regression is distinguished as a good algorithm among the computational intelligence algorithms for all periods between the years 1990 and 2009. 1. Introduction As a natural result of the financial liberalization in the economy and the banking industry in Turkey after 1980s, the competition in the banking industry increased significantly due to the reasons such as many new domestic and foreign players in the banking industry, release of the fund transfers especially from international markets, enabling the banks to make transactions in foreign currencies, advances in the technology, and introducing new services by the banks in the industry. Therefore, a bank, operating in the banking industry, can differentiate itself from the other banks only if it can develop new strategies. In recent years, because of economic and financial crisis, some of the public and private banks were bankrupted and some of them are merged and therefore they were forced to change how they operate. In this instance, a serious competition occurred among the surviving banks to take the market shares of the banks that have left the industry. The banks, which have evaluated the present circumstances, used cutting edge technology, and improved the scope of their products and services, were able to advance forward significantly. Thus, these advances create a necessary environment for such banks to improve their market shares. Therefore, evaluating their position in the market and developing new strategies in accordance with their positions became much more important. The presence of a tough competition between the banks besides the fragile structure of the banking sector in Turkey makes it important to determine the change in the market shares of banks and to take the necessary measures. For this reason, goal-oriented estimations that would be made by using computational
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