Vortex Deconfinement in the XY Model with a Magnetic Field

We study vortex unbinding for the classical two-dimensional XY model in a magnetic field on square and triangular lattices. A renormalization group analysis combined with duality in the model shows that at high temperature and high field, the vortices unbind as the magnetic field is lowered in a two-step process: strings of overturned spins first proliferate and then vortices unbind. The transitions are highly continuous but are not of the Kosterlitz-Thouless type. The unbound vortex fixed point is shown to inherit properties of the underlying lattice, in particular containing a set of nodal lines that reflect the lattice symmetry.Comment: RevTex, 2 column format. 13 figure

Educational Production, Endogenous Peer Group Formation and Class Composition - Evidence from the PISA 2000 Study

The majority of empirical papers in the literature on school quality finds no or only small effects of class size and other school quality measures on students' outcomes. This paper analyses the effect of achievement heterogeneity and therefore the effect of the composition rather than the pure size of the class on student achievement. In this endeavor, individual-level data from an internationally conducted standardized test, the PISA 2000 study is utilized. For the case of US schools the influence of a student's peer group is estimated in a pure endogenous effects model and a model also allowing for contextual effects. The potential endogeneity of peer group formation is addressed in an instrumental variable approach. It turns out that heterogeneous peer groups have a strong detrimental impact on individual achievement. Moreover, it becomes transparent that contextual variables are important for the extent of peer group effects and the endogeneity of peer group formation.peer group effects, learning environment, school quality

The Impact of Economic Integration on Employment – An Assessment in the Context of EU-Enlargement

This paper is motivated by the idea that the enlargement of the European Union is only one part of an overall process, known as economic integration, which characterizes the involvement of European economies into the global division of labor. Therefore, the paper aims at providing a quantitative and qualitative assessment of the impact of economic integration on employment and labor market dynamics in current EU-member and candidate countries. The ultimate aim of this analysis is the provision of forecasts for future labor market developments in the context of EU-enlargement. To this end, we investigate this nexus not only on an economy-wide level, but analyze whether the impact of integration varies for different sectors (automotive and financial services) of the economy. The estimation results suggest that future integration processes lead to an increase of economy-wide employment in the accession countries and a small, if any, rise in this outcome variable in the current EU-countries. Moreover, it could be expected that unemployment rates in the accession countries will decline somewhat, whereas those of the current EU-member states will probably experience an increase. Finally, it is very likely that the structure of employment will shift further towards a higher share of service sector employment.Factor Analysis, Panel Data, Sectoral Case Studies

What Can We Learn From International Student Performance Studies? Some Methodological Remarks

The determinants which are decisive for a successful accumulation of human capital and the transfer of these skills into the labor market are a contentious issue in the literature on the economics of education. Different studies on, for instance, the impact of school resources typically reach different conclusions even if they utilize the same dataset. The reason behind this is that each and every study decisively depends on a set of identification assumptions which are anything but innocuous for the results obtained.This paper aims at clarifying this point by embedding the discussion on the determinants of test success in international performance studies like PISA into a theoretical model of cognitive achievement and an empirical frame of reference.PISA 2000, cognitive achievement, identification

The Effectiveness of Qualification Measures for Employed Workers – An Evaluation Study for Saxony

This paper investigates whether and to what extent employment policy measures (co-) financed by the European Social Fund in Germany meet their objective. Specifically, it is analyzed whether qualification programs for employed workers in the German state of Saxony were effective in terms of employment protection.To this end, a control function approach is implemented which utilizes a unique firm-level dataset. This model explicitly accounts for unobserved heterogeneity between participating and non-participating companies by modeling the participation decision process. Our results suggest a positive effect of program participation. However, this positive treatment effect varies considerably across different sub-groups of the treatment as well as the comparison group.Employment Policy, European Social Fund, Firm-Level Data

Who’s to Blame? The Determinants of German Students’ Achievement in the PISA 2000 Study

The publication of the OECD report on the PISA 2000 study induced a public outcry in Germany. On average, German students participating in this standardized test performed considerably below the OECD average and substantially worse than those of other European countries, like Finland or Ireland. However, the results presented by the report consist mainly of country averages which do not take into account any other covariates of individual student achievement. This paper provides a comprehensive econometric analysis of the association of the individual-level reading test scores of German students with individual and family background information and with characteristics of the school and class of the 15 to 16 year old respondents in Germany to the survey. The results of several quantile regression analyses demonstrate that many popular explanations, like too much regulation of schools or the substantial share of non-citizens among the participating students, are by no means supported by the data. Rather results point towards a considerable impact of schools aiming at a more homogenous body of students in terms of their educational achievement.Student Achievement, School Quality, Quantile Regression.

The Societal Integration of Immigrants in Germany

This paper investigates whether and to what extent immigrants in Germany are integrated into German society by utilizing a variety of qualitative information and subjective data collected in the 1999 wave of the German Socio- Economic Panel (GSOEP).To this end, leisure-time activities and attitudes of native Germans, ethnic Germans and foreign immigrants of different generations are compared. The empirical results suggest that conditional on observable characteristics the activities and attitudes of foreign immigrants from both generations differ much more from those of native Germans than the activities/ attitudes of ethnic Germans. Furthermore, the attitudes of second-generation immigrants tend to be characterized by a larger degree of fatalism, pessimism and self-doubt than those of all other groups, although their activities and participation in societal life resemble more those of native Germans than those of their parents generation.Subjective data, first- and second-generation immigrants, ethnic Germans

Shot Across the Bow, Stigma or Selection? – The Effect of Repeating a Class on Educational Attainment

The German practice of compelling weak students to repeat a class has come under heavy criticism recently. Many observers fear that this practice is, at best, useless or even counterproductive. However, little is known so far on the consequences of having to repeat a class, as compared to be confronted with new course material in the next class.This paper, therefore, aims at generating empirical evidence on the effect of class repetition on individual educational attainment. Since an experimental study is precluded,we utilize an instrumental variable approach to control for unobserved heterogeneity between respondents.Our estimation results suggest that there exists a negative association between repeating a class and educational attainment. However, taking unobserved heterogeneity into account yields a statistically significant and quantitatively substantial positive effect of class repetition on educational outcomes.Schooling Degree, Instrumental Variables Estimation