This thesis focuses on the analysis of heavy-tailed distributions, which are widely applied to model phenomena in many disciplines. The definition of heavy tails based on the theory of regular variation highlights the importance of the tail index, which indicates the existence of moments and characterises the rate at which the tail decays. Two new approaches to make inference for the tail index are proposed. The first approach employs a regression technique and constructs an estimator of the tail index. It exploits the fact that the behaviour of the characteristic function near the origin reflects the behaviour of the distribution function at infinity. The main advantage of this approach is that it utilises all observations to constitute each point in the regression, not just extreme values. Moreover, the approach does not rely on prior information on the starting point of the tail behaviour of the underlying distribution and shows excellent performance in a wide range of cases: Pareto distributions, heavy-tailed distributions with a non-constant slowly varying factor, and composite distributions with heavy tails. The second approach is motivated by the asymptotic properties of a special moment statistic, the so-called partition function. This statistic considers blocks of data and is generally used in the context of multifractality. Due to the interplay between the weak law of large numbers and the generalised central limit theorem, the asymptotic behaviour of the partition function is strongly affected by the existence of moments even for weakly dependent samples. Via a quantity, the scaling function, a graphical method to identify the existence of heavy tails is proposed. Moreover, the plot of the scaling function allows one to make inference for the underlying distribution: with infinite variance, finite variance with tail index larger than two, or all moments finite. Furthermore, since the tail index is reflected at the breakpoint of the plot of the scaling function, this gives the possibility to estimate the tail index. Both these two approaches use the entire distribution, not just the tail, to analyse the tail behaviour. This sheds a new light on the analysis of heavy-tailed distributions. At the end of this thesis, these two approaches are used to detect power laws in empirical data sets from a variety of fields and contribute to the debate on whether city sizes are better approximated by a power law or a log-normal distribution.

Despite the great efforts scholars have devoted to the study of migration a unified and coherent theory of international migration does not yet exist. Particularly, only in recent years, scholars have developed models of labor mobility to take into account social interaction across agents. Similarly, empirical analysis lacks an adequate approach to social interaction in migration, often using very rough measures as, for example, the stock of compatriots in the receiving country. The aim of this dissertation is to examine economic migrants decision to migrate, focusing specifically on potential migrants who can choose if and where to migrate, and which conditions facilitate their migration. It investigates how wealth, social networks and education interact in determining householdsâ€TM migration strategies and the aggregate dimension and composition of migration flows. Household income maximization strategy evaluates migration as a possible, but costly investment. In a context of underdeveloped financial and insurance markets, budget constraints play a key role in determining migration behavior. Poorer households have higher incentives, but fewer opportunities to migrate, whereas better-off households have fewer incentives, but greater possibilities of migrating. Social networks, reducing costs and risks of migration and thus counterbalancing budget constraints, mitigate this effect and allow new social strata to migrate. In the empirical analysis we examine Mexican migration to the U.S., proposing two new tools to apply in empirical analysis and showing that household and community networks act as complements in the probability of migration, and as substitutes in the optimal number of migrants. We also examine migration to the U.S. from five Central American countries, comparing findings with those obtained for Mexico.

The idea that public debt may represent a burden for the economic system as a whole has distant origins and focuses on who and how should pay for debt, and with what consequences on the economy. Nevertheless, particularly influential both for academic research and the implementation of the fiscal corrective policies was the empirical paper proposed by Reinhart and Rogoff in 2010 at the dawn of the crisis. Reinhart and Rogoff (2010), in a large panel of countries, identified a critical threshold of 90% of the debt-to-GDP ratio beyond which debt is harmful to growth. Several countries in the world were fast approaching that threshold or already were well beyond it. Though Reinhart and Rogoff’s work was affected by many flaws, it has spurred buoyant empirical research in search of the general debt thresholds above which growth is jeopardised by public debt. Further works have supported the existence of critical debt-to-GDP ratios under various time and space observational fields, but results of these researches are inconclusive or controversial, as discussed in Chapter 2. Country-specific characteristics and contingencies play in fact a prominent role, thus prompting a branch of literature that attempts to comprehensively understand the debt-growth relationship and its determinants (see for instance Panizza and Presbitero, 2014; Eberhardt and Presbitero, 2015). In contrast with the findings of the broad threshold literature and of many theoretical models, the idea that public debt is always harmful to economic growth has partially been reconsidered in the last few years. Nevertheless, the existence of a linkage between debt and growth has not been rejected: the long-run relationship between such macroeconomic variables is inevitably and broadly affected by heterogeneous factors. However, in retrospect and as emerges in Chapter 1, one may say that the empirical pursuit of the debt-to-GDP threshold harmful to growth lacks deeper foundational work: why should we expect a negative public debt-growth relationship? In addition, if such a relationship exists, why should it take the specific form of a threshold of the debt-to-GDP ratio, and why should we expect this threshold to be equally valid across time and space? These questions are the starting point of this Doctoral Thesis, which is organised as follows. Chapter 1 surveys the theoretical literature concerning public debt and economic growth, aiming at finding a theoretical foundation for the debt-threshold literature. Overall, there is no clear and straightforward answer to the questions of why we should expect a negative public debt-growth relationship in the first place, why it should take the specific form of a threshold of the debt-to-GDP ratio, and why we should expect this threshold to be equally valid across time and space. Or, from another perspective, there are many possible answers and many elements affecting them, thus reflecting the complexity of the argument, as well as the variety of the empirical situations. In particular, the literature that I examine, on the one hand offers a rich variety of explanations and insights to researchers of the debt-growth relationship but, on the other, it does not provide any one-way conclusion: the relationship may be negative, positive, or even no relationship may exist, both from a theoretical and an empirical point of view. Even less is theoretically founded the existence of a general debt-to-GDP threshold above which growth is consistently stifled. Each country’s specific characteristics, circumstances, and events have an overwhelming importance that cannot be encapsulated in a single general law. In Chapter 1, I also present a fiscal model of endogenous growth that may help address the theoretical issues in an orderly and consistent manner along two specific coordinates of debt assessment: sustainability/unsustainability, and efficiency/inefficiency. The thrust of the model is that no meaningful assessment of debt and its effect on growth at any point in time is possible without reference to the whole debt trajectory and the specific state of the economy along the trajectory. Chapter 2 reviews the empirical literature and focuses on the debt-growth relationship from an econometric point of view. As before, it is difficult to derive a univocal conclusion on the nature of such a relationship on the basis of the literature’s findings: the existence of a significant negative relationship between debt and growth is the predominant thinking, though in contrast with the conclusions of several works. For these reasons, the aim of Chapter 2 is to go to the roots of the debt-growth relationship, to investigate whether the outstanding debt and the GDP are linked. To this end, I have adopted a research methodology that differs from the most common employed in the literature on debt-to-GDP thresholds. First, my analysis does not hinge on any specific theory, and it should not be considered as a proof of a specific theoretical statement. Rather, it is based on the approach outlined by Hoover et al. (2008) and aims at understanding "what the data say" without imposing aprioristic theoretical structures. A second methodological choice consistent with this approach is to treat the (growth of the) amount of public debt and (the growth of) GDP as the two genuine primitives, without imposing the debt-to-GDP ratio as a primitive itself. In fact, for this to be possible, the two underlying primitives should display well defend statistical properties, namely cointegration and convergence towards a long-term equilibrium value, which are usually not tested in the literature. Third, I believe that the heterogeneity, or non-generality, of results that I have pointed out before should be taken as an intrinsic feature of the problem at hand, so that a viable strategy is to restrict, rather than expand, the observational field. I have set time and space limits to my dataset by purpose: my analysis is based on a panel dataset including quarterly data for 25 Eastern and Western European countries from 1999Q1 to 2015Q4. The Eurozone represents a unique "field experiment" of a large number of countries where some key conditioning factors of fiscal policy are common and exogenous, namely fiscal targets and rules, monetary policy, and the exchange rate with the rest of the world. The main result is that a long-run equilibrium relationship between GDP and debt exists for some countries ? and debt and GDP tend to adjust towards it ? but it is not generalisable. Where a relationship exists, it does not always imply that the debt-to-GDP ratio may be the appropriate variable for describing it. Moreover, cross-country heterogeneity and the role of the financial crisis and of the austerity periods remain substantial and overwhelming factors. Therefore, a unique equation describing the GDP-debt relationship does not seem to exist, which entails the impossibility to derive a meaningful general debt-to-GDP threshold. Thus far I have focused on the general relationship between debt and growth from both the theoretical and the empirical points of view. Turning to the analysis of the Sovereign Debt Crisis and of the austerity period, Chapter 3 attempts to explain what has driven austerity ? measured as the first difference of the cyclically adjusted structural primary balance ? within a dataset of 28 European countries. In the first part of this chapter I present a correlation analysis that describes the relationship between the variable austerity and each of the considered determinants, that are brought back to four main sets of variables: fiscal discipline, market discipline, fiscal consolidation, and macroeconomic stabilisation. The second part implements a panel econometric analysis based on the principal component factor analysis and on the pooled partial common correlation effect estimator. Results show that the variables and factors of the analysis are not able to fully explain austerity, though an important contribution is provided by the enforcement of the Eurozone fiscal rules (the adoption of excessive deficit procedures) and is partially counterbalanced by the cyclical position of the economy. The last chapter, Chapter 4, aims at gaining insight into the role of debt and government expectations and their impact on growth under uncertainty conditions. In fact, it is possible that the effects of austerity measures in some countries, for instance the so-called PIIGS, were amplified by uncertainty. My ambition is to relate austerity with consumers’ expectations, thus studying whether and when consumers’ beliefs about public debt and government intervention affect their consumption, savings, and tax compliance choices with a direct impact, at the aggregate level, on economic growth. Therefore, Chapter 4 implements a laboratory experiment to study how people react in a generalized framework in which public debt may be unexpectedly reduced. The debt dynamics arises endogenously: within a public good game, taxes are collected from all participants and are used to cover a given level of public expenditure, which is then equally distributed to the same participants at the beginning of each round. If the collected amount of taxes is lower than what the public expenditure would require, a deficit is generated. Moreover, reproducing a forced withdrawal, the outstanding amount of public debt can be reduced upon accessing subjects’ savings. Within this setting, expectations are directly elicited by asking subjects if they believe that public debt is going to be reduced, and if they think that the other subjects believe that public debt is sustainable. Therefore, it is possible to identify whether and how agents’ allocations and expectations are affected by the public debt path. As mentioned above, a peculiarity of my approach is the endogenous dynamics of public debt: not only it avoids introducing predetermined dynamics, but also increases the ecological validity of the experiment. Participants are indeed more psychologically involved in the debt mechanism and they might feel responsible for the raise in debt. On the other hand, an exogenous dynamics could depict public debt and tax compliance as irrelevant. Results show that this experimental framework is characterized by relatively high and often increasing aggregate savings and relatively low and decreasing aggregate consumption. Interestingly, an increase in the debt-reduction expectations and a decrease in the perceived debt sustainability are also found to explain savings and consumption behaviours, as is shown in the econometric part of Chapter 4.

This thesis examines three main themes, firms productive efficiency, internationalisation of African firms, and effect of liberalisation policies on market power and market imperfections. The thesis combines two main strands in economics literature in accessing the three main themes of the papers. The first strand regards methodological approaches to estimate a production function from which productive efficiency can be computed. Consistent estimation of productive efficiency is a necessary condition to analyse firm behaviour and their response to trade policies. The thesis critically examines methodologies to estimate productive efficiency. The second strand, international trade and industrial development, analyse firms behaviour in foreign market as well as firms responses to trade liberalisation policies and their overall impact on structural transformation. The two strands of literature examined in this thesis resulted in three independent papers, each of which addresses specific issues along the spectrum of productive efficiency estimation, internationalisation, and market power.

This thesis contains four closely related essays which address the empirical issues pertaining to the causes, consequences, and households’ responses to food price shocks in Uganda. The first essay investigates the nature of volatilities in agricultural commodity prices in Uganda between 2000 and 2012 by focusing on six key food staples, namely matooke, cassava, maize, sweet potatoes, beans, and millet flour. It studies the behavior of monthly price volatilities of these commodities, examines the extent of their volatility spillovers, identifies their macroeconomic and environmental drivers, and uncover their differential impacts using respectively the General Autoregressive Conditional Heteroscedastic (GARCH), the Vector Autoregressive (VAR) and the Seemingly Unrelated Regression (SUR) models. I find evidence that both unconditional and conditional price volatilities have significantly increased since January 2008 for most commodities, period of turmoil in the global food markets. The GARCH (1, 1) estimates indicate a strong persistence in volatility for most commodities while results from the Exponential GARCH (1, 1) models suggest the presence of asymmetric and leverage effects of unexpected price shocks for half of the commodities. In addition, the VAR estimation results detect limited and mostly unidirectional spillover effects across food commodities. Finally, historical price volatilities of most commodities are found to be primarily affected by volatilities in consumer price indices, fuel prices, and rainfall, with less evidence of strong seasonality effects as previously reported. The second essay presents an empirical analysis of the welfare impacts of food price changes in Uganda using three waves of the Uganda National Panel Surveys (UNPS) spanning over the years 2005-2011. It theoretically investigates the implications of labor market imperfections and households’ heterogeneity in terms of their net positions in both food and labor markets and compares welfare estimates between separable and non-separable models. Through the estimations a panel stochastic production frontier function and a censored-Quadratic Almost Ideal Demand Systems (QUAIDS) with expenditure and shadow wage endogeneities, the results suggest that the welfare effects of price changes (measured in terms of compensating variations) were globally lower in the non-separable agricultural model, implying a high degree of labor market frictions. Furthermore, I find that the welfare effects were unevenly distributed both within and between household groups. Particularly, although agricultural households benefited from price increases as a group between 2005/6 and 2009/10, both significant and insignificant net buyers did suffer from price changes. Moreover, results from non-parametric estimations show that households at the extremes of the welfare distribution were more severely hit by food price instabilities than others. Finally, the essay suggests that the important dynamics in the net market positions observed during the sample period might be attributed to a cost-benefit analysis related to the potential welfare effects of food prices. The third essay explores the question of crop choices and land allocations in environments where farmers face uncertainties about end-of-season output prices and yield levels, weather variability, and formulate expectations about their future levels. Indeed, in the absence of credit and/or insurance markets, farmers are widely expected to adjust their land allocation decisions as a management tool against agricultural and market-related risks. However, little is actually known about the likely differential effects of each of these risk components on farmers’ decisions, particularly when current decisions are allowed to depend on previous choices. Using a nationally representative panel data set for agricultural households in Uganda spanning over the years 2005 – 2012, the paper proposes to investigate the role played by both price and yield risks on farmers’ crop choices and area allocations using a multivariate generalization of the Heckman-type two-step procedure: a multivariate crop selection and a conditional acreage share models. The crop selection problem is modeled as a dynamic multivariate probit regression and estimated through Simulated Maximum Likelihood and the Geweke Hajivassiliou Keane simulator, whereas the conditional acreage share model is estimated using a dynamic multivariate fractional logit model. In both the multivariate crop selection and acreage share models, the results reveal that, while own expected prices and yields are among the main drivers of farmers' crop choices and land share allocations, farmers are found to be more sensitive to changes in expected yield levels than in expected end-of-season output prices. In addition, yield risks, temperature and rainfall volatility appear to have more impact on acreage share decisions than market price risks. Finally, household characteristics are found to play a marginal role in explaining farmers’ crop selection and acreage allocation decisions. The fourth and last essay develops a modified standard Ramsey model to analyze households’ welfare growth and test the assumption that differential exposure to food price shocks leads to different welfare trajectories and to potentially increased risks of poverty traps. The essay focuses on two welfare indicators, namely consumption levels and asset indices, and employs a battery of econometric methods, ranging from parametric GMM fixed effects models to locally weighted scatterplot smoother (LOWESS), local polynomial regressions, and Ruppert et al’s (2003) semi-parametric penalized splines to address nonlinearities in welfare dynamics, identify and locate critical welfare thresholds, and test for the presence of single against multiple welfare equilibria. Using the full sample, I find nonlinearities in welfare dynamic paths and reduction in the growth rates of both consumption levels and assets holdings as a consequence of exposure to food price and asset shocks. However, there is no evidence of poverty traps caused by households’ exposure or vulnerability to food price shocks, but instead I identify only a single dynamic stable equilibrium, located slightly above the official poverty, towards which Ugandan households are converging in the long run. Finally, when disaggregating households into different sub-groups sharing similar characteristics, the empirical results reveal that Ugandan households are converging towards specific welfare equilibria, depending on their initial conditions, demographic characteristics, the extent of their vulnerability and differential exposure to food price shocks. Particularly, I found that, households exposed to food price shocks or above the vulnerability threshold index are expected to move in the long run to welfare equilibria located at lower levels than their unexposed or less vulnerable counterparts.

This thesis includes three main chapters that are the outcome of different research projects. All chapters stand as independent papers, but they are linked by the common focus on firm financial factors and export behavior, and by the use of microeconometric methodologies applied to firm-level data. The first two chapters investigate, respectively, the impact of export activity on firms’ access to credit and the role of corporate financial structure as a determinant of exporters’ ability to compete on foreign markets through quality. The third chapter looks instead at the scope for promoting investment and exports of small and medium enterprises through the introduction of more favorable Corporate Taxation rates.

Improving agricultural productivity, agricultural commercialization and improving the livelihoods of the population are the main challenges in the Sub-Saharan Africa region where the majority of the population are poor and live in rural areas. Several factors including lack of improved farming practices, poor infrastructure, low level of market integration to the world market and within countries, climate change, and inadequate policy support restrained the performance of the agricultural sector in the region. This thesis consists of four chapters, three empirical and one theoretical chapter. Each of the empirical chapters deals with selected topics pertinent to the agriculture sector in Ethiopia. The theoretical chapter reviews the agricultural policies adopted by the existing government and implemented over the past two decades. After the introductory chapter, the second chapter analyzes the impacts of climate change on crop yields and yield vari-ability in Ethiopia. The impacts of climate change appear to be different across crops and regions. However, the future crop yield levels largely depend on future technological development in farming practices. The third chapter aims to understand the extent of price transmissions from the world markets to domestic grain markets, and the extent of market integration in domestic grain markets. The fourth chapter investigates and compares the volatilities of oilseeds prices in the world and domestic markets. The data used in the second, third and fourth chapters are obtained from various secondary sources. The fifth chapter reviews major agricultural policies implemented over the last two decades and identifies policies that either enhanced the growth of the agricultural sector or holding back its performance. The sixth chapter underlines the main conclusions and indicates future research areas.

This thesis is made up of four chapters on productivity and efficiency analysis. The first chapter is a critical review of theoretical and empirical literatures related to this broad field, which has attracted a considerable amount of economic research in the last years; the other three chapters are original contributions in different directions. Chapter 2 consists of an extensive Monte Carlo exercise on the misspecification of the inefficiency distribution in stochastic frontier models, Chapter 3 investigates, both theoretically and empirically, the relationship between vertical integration and firm efficiency in the Italian machine tool industry, and, finally, Chapter 4 sheds light on the effect of both inward and outward foreign direct investments on regional productivity growth in Europe. Although each chapter has its own independence, two features characterize the entire thesis: the detection of large differences in production performance both at the micro and aggregate level, and the attempt to relate these differences to other aspects of the production units, starting from economic theory.

This thesis examines the relationship between environmental regulation, innovation, and competitiveness. Specifically, it investigates the impact of regulatory stringency on innovation in the chemical industry by analyzing the evolution of innovative activity in highly regulated technological areas in the European Union from 1976 to 2003. A direct quantitative measure of regulatory impact on innovation was constructed by transforming the economic measurement problem into a technological classification issue. The specific regulation investigated was the EU Council Directive 76/769/EEC, which contains 986 restrictions imposed on the marketing and use of 939 chemical substances. These restrictions were linked to 17 technological fields in the International Patent Classification. The data on patent applications was extracted from the ESPACE Bulletin database maintained by the European Patent Office. Given the increasing regulatory stringency, four questions were investigated: Did regulation spur patenting activity? Has there been a change in the geographical origin of patents? Has there been an increase in patenting concentration? Has there been a change in the direction of the patenting trend? These issues were examined at the aggregated level using descriptive statistics, panel data regressions, and the study of technological trend. Four case studies were conducted to illustrate strategies utilized by European and non-European firms. I found that most restrictions were imposed during the years of 1997 and 2003 and affected mainly technological areas associated with agrochemicals, polymers, and paints and dyes. In overall regulatory stringency impacted positively patenting activity. However, top players were impacted negatively. Consequently, there was a reduction in the concentration of innovative activity in highly regulated technological areas. Ma jor changes occurred in areas in which the largest number of restrictions were imposed. There was an overall increase in innovations associated with new processes and formulations, indicating increased incremental innovation and a shift from patenting in regulated to non-regulated applications. Hence, there was increasing patenting activity in areas that did not depend on novel substances or did not have an opportunity to innovate in non-regulated uses. By contrast, there was a sharp fall in the number of applications in areas in which these conditions did not exist. Two explanations for these results are proposed: “new” technologies benefit from regulatory stringency while “old” technologies are discouraged; regulation spurs the development of substitutes better adapted to the actual regulatory framework. Moreover, this thesis shows that the Porter hypothesis is supported for the chemical industry. Yet, this occurs not because firms innovate under more stringent regulation, but because it stimulates new entrants in the market of innovation.