Broadening the income tax base in the context of tax reform in Türkiye: A comparative analysis and assessment of policy options

In recent discussions on tax reform within the Turkish Tax System, the expansion of the tax base, as one of the fundamental objectives of the reform, has consistently come to the fore. In this thesis, the issue of expanding the tax base has been examined in detail within the context of income tax, and contributions to the topic through new and distinct theoretical and practical proposals have been aimed. The thesis consists of three main chapters. In the first chapter, the findings of the literature review on the expansion of the income tax base within the framework of tax reform and its objectives are presented together with new and original definitions within the theoretical framework. In the second chapter, tax reforms aimed at expanding the income tax base in different countries, as well as reforms and regulations affecting the income tax base in Turkey, are analyzed comparatively, and the general overview of the income tax base in Turkey is discussed. In the third chapter, well-founded proposals for expanding the income tax base in the Turkish Tax System are developed, and findings regarding the use of artificial intelligence algorithms in identifying high-risk taxpayers who may engage in unregistered income-generating activities or tax evasion are also discussed. As a result of the research, the practices of countries that have implemented tax reforms aimed at expanding the income tax base have been evaluated comparatively in terms of their applicability to the Turkish Tax System. Based on practical experience and research findings, well-founded proposals have been presented; moreover, it has been shown that the use of certain artificial intelligence/machine learning algorithms can be applied with high accuracy in identifying high-risk taxpayers who may engage in tax evasion.