This thesis consists of three extended essays on the evasion of income tax. The main purpose of this thesis is to refine the existing tax evasion models in a way that makes it possible to explain empirically established stylized facts that could not be explained before. In the first part we use a standard neoclassical framework in order to analyse the impact of risk preferences on evasion behaviour. We argue that expected value maximization with some fixed and variable costs incurred during the evasion process (moral cost, cost of coverage action etc.) is an appropriate framework to explain the stylised fact that higher tax rates and a higher income lead to more tax evasion. This resolves one of the puzzles concerning tax evasion that was unsolved so far. The second part uses this finding to examine the effect of tax rates on the resources wasted during the process of tax sheltering and evasion detection. We model a declaration detection process, where both, tax inspector and taxpayer, can invest into the probability that the true income from different potential income sources is verified We show that in this contest a higher tax rate leads to more resources that are waste- fully invested in the cat and dog play between authority and taxpayer. The positive effect of rising tax rates and rising income on tax evasion is maintained. The final part of the thesis explains why the tax authority in reality audits sequentially. I.e. it audits single sources at the beginning to conduct a full-scale audit, whenever it finds evidence for irregularities. To do so, we use a simplified version of the model from part two and allow for sequential auditing as well as for different types of taxpayers. The possibility to learn something about the type of the taxpayer by auditing sequentially gives the authority a powerful tool to better target its detection effort. Sequential auditing therefore reduces the amount of non-filers and black market participants as well as the probability that somebody evades a fraction of his total income.

Σύμφωνα με έρευνες που πραγματοποιήθηκαν τα τελευταία χρόνια, παρατηρείται μια αύξηση της φοροδιαφυγής όχι μόνο σε παγκόσμιο επίπεδο αλλά και στον ελληνικό χώρο. Το γεγονός αυτό δείχνει τη δυσαρέσκεια και τη δυσκολία των εταιριών να ανταπεξέλθουν στους υπάρχοντες φορολογικούς νόμους αλλά και την επιδίωξης τους να αυξήσουν τα κέρδη τους με όχι νόμιμο όμως τρόπο. Στην παρούσα εργασία γίνεται ανάλυση του φορολογικού συστήματος στην Ελλάδα και των κινήτρων που ωθούν τις επιχειρήσεις στη φοροδιαφυγή, ενώ διερευνάται η σχέση ανάμεσα στους φορολογικούς ελέγχους χρήσεως και σε άλλα στοιχεία χρηματοοικονομικών καταστάσεων των εταιριών. Βασιζόμενοι σε εμπειρική έρευνα σε ευρύ δείγμα επιχειρήσεων για την τριετία 2008-2010 οδηγούμαστε στο συμπέρασμα ότι το ύψος της φοροδιαφυγής που επικρατεί στην Ελλάδα έχει μεγάλες διαστάσεις και συνδέεται με συγκεκριμένα εταιρικά χαρακτηριστικά. / According to surveys carried out in recent years, there is an increase in tax evasion not only globally but also in the Greek area. This indicates dissatisfaction and difficulty for companies to cope in existing tax laws and the pursuit to increase their profits with no legitimate way though.

Depuis le modèle de référence développé par Allingham et Sandmo (1972), les problèmes liés à la fraude fiscale et particulièrement au lien entre les raisons de conformité fiscale et le montant du revenu déclaré ont été souvent étudiées. La décision du contribuable dépend essentiellement du montant de son revenu réel, du taux d'imposition fiscale, de la probabilité de contrôle, du montant des amendes infligées en cas de détection. Mais d'autres paramètres plus psychologiques qu'économiques sont aussi tenus en compte à savoir le climat social auquel le contribuable évolue, l'utilisation de leurs cotisations par le gouvernement, les normes sociales, ou tout simplement la conscience du devoir fiscal pour le financement des biens publics et du civisme fiscal. Ces faits ne sont essentiellement pas tenus en compte dans un pays en développement comme Madagascar. La fraude fiscale est liée à l'incapacité de l'administration fiscale à assurer pleinement le système de contrôle par manque de moyens et des phénomènes comme la corruption, la présence accrue du secteur informel, l'influence des décideurs politiques. Les études empiriques ont montré que la Taxe sur la Valeur Ajoutée (TVA) reste l'impôt le plus fraudé par les contribuables et que les pertes annuelles pour cause de fraude fiscale sont exorbitantes, avec un montant total avoisinant les 203 millions d'€ de 2007 à 2009 dans les centres enquêtés. / Since the reference model was developed by Allingham and Sandmo (1972), the problems linked ta tax evasion and particularly ta the relationship between the reasons for tax compliance, and the amount of declared income have often been studied. The taxpayer's decision depends primarily on the amount of his real income, on the tax rate, on the probability of control and on the amount of the fines in the case of identified fraud. However, other parameters more psychological than economical arc also taken into account ta identify the social climate in which the taxpayer evolves, the use of their tax contributions by the government, the social norms, or simply the awareness of the duty taxes in order ta support public projects and fiscal public­spiritedness. These facts have not yet been taken into consideration in developing countries like Madagascar. Tax evasion is linked to the incapacity of tax authorities to ensure full control of the system due to a lack of means as well as phenomena such as com1ption, the increasing presence of the informal sector and the influence of the political decision makers. Empirical studies have shown that Value-Added Tax remains the most defraudcd tax by taxpayers and that the annual lasses due to tax evasion are exorbitant, totaling around € 203 million from 2007 to 2009 in the centers participating in the survey.