Essays in Macroeconomics

This thesis consists of three independent chapters which deal with macroeconomic topics that drew much attention in the years of financial and economic crisis since 2007. Chapter 1 analyzes how the availability of financial assistance by international lenders, like the International Monetary Fund (IMF), affects the default incentives of a government. The analysis is done using a quantitative model of sovereign default. In this model a default is the optimal decision of the government and can be induced either by bad fundamentals or by self-fulfilling crises due to runs by international investors. Financial assistance is provided by an official lender. It is senior to market debt and associated with conditionality in the form of debt targets. The quantitative analysis, for which the model is calibrated to match Argentinean data, shows that the probability of a default on market debt is higher when financial assistance is available. This result can be explained by the fact, that the financial assistance works as an insurance for the investors. For given fundamentals the government is less likely to default when it has the possibility to receive financial assistance. However, there is a counteracting general equilibrium effect. Given the smaller default risk, the investors are willing to pay a higher price for government bonds. This in turn induces the government to borrow more. The resulting higher average debt levels then lead to more defaults in equilibrium. Chapter 2 also deals with the topic of sovereign default. It analyzes to what extent a standard quantitative model of sovereign default can explain the developments of sovereign interest rate spreads observed for European countries during the crisis in the recent years. More specifically, the model is used to analyze the case of Italy in the time of the crisis on the European sovereign debt markets. The model features default as the optimal decision of the government, includes long-term debt and allows for self-fulfilling default crises. For the quantitative analysis the model is calibrated to match important moments of the Italian data. The analysis shows that while the model is able to match some aspects of the data, it predicts a counterfactual default in the early periods of the crisis, when output was extremely low. Furthermore, the quantitative results suggest that the development of the interest rate spreads are influenced by other factors than only the Italian fundamentals. Interestingly, the long maturity of Italian debt leaves only little room for self-fulfilling crises as considered in the model. Chapter 3 turns to a different topic that has played an important role in the analysis of the financial and economic crisis. Using vector autoregressive (VAR) models, the chapter provides an empirical analysis of the effects of monetary policy shocks and credit shocks on house prices and the broader economy in the United States and the United Kingdom. The shocks are identified using sign restrictions derived from the impulse response functions of a dynamic stochastic general equilibrium (DSGE) model that includes house prices and collateralized credit. The empirical analysis shows that in the U.S. a negative monetary shock leads to a decline in house prices, while there is no clear effect in the U.K. The credit shock, in contrast, has no significant effect on house prices when U.S. data is considered, but has a short-term negative effect in the U.K. The chapter also provides a historical decomposition to shed light on the role of credit and monetary shocks for house price developments

Real-time soft shadows using a single light sample

We present a real-time rendering algorithm that generates soft shadows of dynamic scenes using a single light sample. As a depth-map algorithm it can handle arbitrary shadowed surfaces. The shadow-casting surfaces, however, should satisfy a few geometric properties to prevent artifacts. Our algorithm is based on a bivariate attenuation function, whose result modulates the intensity of a light causing shadows. The first argument specifies the distance of the occluding point to the shadowed point; the second argument measures how deep the shadowed point is inside the shadow. The attenuation function can be implemented using dependent texture accesses; the complete implementation of the algorithm can be accelerated by today's graphics hardware. We outline the implementation, and discuss details of artifact prevention and filtering

Validating a pain assessment tool in heterogeneous ICU patients: Is it possible?

Non-communicative adult ICU patients are vulnerable to inadequate pain management with potentially severe consequences. In German-speaking countries, there is limited availability of a validated pain assessment tool for this population. Aim The aim of this observational study was to test the German version of the Critical-Care Pain Observation Tool (CPOT) in a heterogeneous adult ICU population. Methods The CPOT's feasibility for clinical use was evaluated via a questionnaire. For validity and reliability testing, the CPOT was compared with the Behavioural Pain Scale (BPS) and patient's self-report in 60 patients during 480 observations simultaneously performed by two raters. Results The feasibility evaluation demonstrated high satisfaction with clinical usability (85% of responses 4 or 5 on a 5-point Likert scale). The CPOT revealed excellent criterion validity [agreement between CPOT and BPS 94.0%, correlation of CPOT and BPS sum scores r = 0.91 (P < .05), agreement of CPOT with patient self-report 81.4%], good discriminant validity [mean difference of CPOT scores between at rest and non-painful stimulus 0.33 (P < .029), mean difference of CPOT scores between at rest, and painful stimulus 2.19 (P < .001)], for a CPOT cut-off score of >2 a high sensitivity and specificity (93% and 84%), high positive predictive value (85%), and a high negative predictive value (93%). The CPOT showed acceptable internal consistency (Cronbach's alpha 0.79) and high inter-rater reliability [90% agreement, no differences in CPOT sum scores in 64.2% of observations, and correlation for CPOT sum scores r = 0.72 (P < .05)]. Self-report obtained in patients with delirium did not correlate with the CPOT rating in 62% of patients. Conclusion This is the first validation study of the CPOT evaluating all of the described validity dimensions, including feasibility, at once. The results are congruent with previous validations of the CPOT with homogeneous samples and show that it is possible to validate a tool with a heterogeneous sample. Further research should be done to improve pain assessment and treatment in ICU patients with delirium

Discretized Gravity in 6D Warped Space

We consider discretized gravity in six dimensions, where the two extra dimensions have been compactified on a hyperbolic disk of constant curvature. We analyze different realizations of lattice gravity on the disk at the level of an effective field theory for massive gravitons. It is shown that the observed strong coupling scale of lattice gravity in discretized five-dimensional flat or warped space can be increased when the latticized fifth dimension is wrapped around a hyperbolic disk that has a non-trivial warp factor. As an application, we also discuss the generation of naturally small Dirac neutrino masses via a discrete volume suppression mechanism and discuss briefly collider implications of our model.Comment: 35 pages, 10 figures, typos corrected. Matches final version published in Nucl.Phys.B781,32-63,200

An International Consensus to Standardize Integration of Histopathology in Ulcerative Colitis Clinical Trials

Background & Aims: Histopathology is an emerging treatment target in ulcerative colitis (UC) clinical trials. Our aim was to provide guidance on standardizing biopsy collection protocols, identifying optimal evaluative indices, and defining thresholds for histologic response and remission after treatment. Methods: An international, interdisciplinary expert panel of 19 gastroenterologists and gastrointestinal pathologists was assembled. A modified RAND/University of California, Los Angeles appropriateness methodology was used to address relevant issues. A total of 138 statements were derived from a systematic review of the literature and expert opinion. Each statement was anonymously rated as appropriate, uncertain, or inappropriate using a 9-point scale. Survey results were reviewed and discussed before a second round of voting. Results: Histologic measurements collected using a uniform biopsy strategy are important for assessing disease activity and determining therapeutic efficacy in UC clinical trials. Multiple biopsy strategies were deemed acceptable, including segmental biopsies collected according to the endoscopic appearance. Biopsies should be scored for architectural change, lamina propria chronic inflammation, basal plasmacytosis, lamina propria and epithelial neutrophils, epithelial damage, and erosions/ulcerations. The Geboes score, Robarts Histopathology Index, and Nancy Index were considered appropriate for assessing histologic activity; use of the modified Riley score and Harpaz Index were uncertain. Histologic activity at baseline should be required for enrollment, recognizing this carries operational implications. Achievement of histologic improvement or remission was considered an appropriate and realistic therapeutic target. Current histologic indices require validation for pediatric populations. Conclusions: These recommendations provide a framework for standardized implementation of histopathology in UC trials. Additional work is required to address operational considerations and areas of uncertainty

Measurement of Longitudinal Spin Transfer to Lambda Hyperons in Deep-Inelastic Lepton Scattering

Spin transfer in deep-inelastic Lambda electroproduction has been studied with the HERMES detector using the 27.6 GeV polarized positron beam in the HERA storage ring. For an average fractional energy transfer = 0.45, the longitudinal spin transfer from the virtual photon to the Lambda has been extracted. The spin transfer along the Lambda momentum direction is found to be 0.11 +/- 0.17 (stat) +/- 0.03 (sys); similar values are found for other possible choices for the longitudinal spin direction of the Lambda. This result is the most precise value obtained to date from deep-inelastic scattering with charged lepton beams, and is sensitive to polarized up quark fragmentation to hyperon states. The experimental result is found to be in general agreement with various models of the Lambda spin content, and is consistent with the assumption of helicity conservation in the fragmentation process.Comment: 8 pages, 3 figures; new version has an expanded discussion and small format change

Flavor Decomposition of the Polarized Quark Distributions in the Nucleon from Inclusive and Semi-inclusive Deep-inelastic Scattering

Spin asymmetries of semi-inclusive cross sections for the production of positively and negatively charged hadrons have been measured in deep-inelastic scattering of polarized positrons on polarized hydrogen and 3He targets, in the kinematic range 0.023<x<0.6 and 1 GeV^2<Q^2<10 GeV^2. Polarized quark distributions are extracted as a function of x for up $(u+u_bar) and down (d+d_bar) flavors. The up quark polarization is positive and the down quark polarization is negative in the measured range. The polarization of the sea is compatible with zero. The first moments of the polarized quark distributions are presented. The isospin non-singlet combination Delta_q_3 is consistent with the prediction based on the Bjorken sum rule. The moments of the polarized quark distributions are compared to predictions based on SU(3)_f flavor symmetry and to a prediction from lattice QCD.Comment: 14 pages, 6 figures (eps format), 10 tables in Latex New version contains tables of asymmetries and correlation matri

Antidepressant Response in Major Depressive Disorder: A Meta-Regression Comparison of Randomized Controlled Trials and Observational Studies

To compare response to antidepressants between randomized controlled trials (RCTs) and observational trials.Published and unpublished studies (from 1989 to 2009) were searched for by 2 reviewers on Medline, the Cochrane library, Embase, clinicaltrials.gov, Current Controlled Trial, bibliographies and by mailing key organisations and researchers. RCTs and observational studies on fluoxetine or venlafaxine in first-line treatment for major depressive disorder reported in English, French or Spanish language were included in the main analysis. Studies including patients from a wider spectrum of depressive disorders (anxious depression, minor depressive episode, dysthymia) were added in a second analysis. The main outcome was the pre-/post-treatment difference on depression scales standardised to 100 (17-item or 21-item Hamilton Rating Scale for Depression or Montgomery and Åsberg Rating Scale) in each study arm. A meta-regression was conducted to adjust the comparison between observational studies and RCTs on treatment type, study characteristics and average patient characteristics. 12 observational studies and 109 RCTs involving 6757 and 11035 patients in 12 and 149 arms were included in the main analysis. Meta-regression showed that the standardised treatment response in RCTs is greater by a magnitude of 4.59 (2.61 to 6.56). Study characteristics were related to standardised treatment response, positively (study duration, number of follow-up assessments, outpatients versus inpatients, per protocol analysis versus intention to treat analysis) or negatively (blinded design, placebo design). At patient level, response increased with baseline severity and decreased with age. Results of the second analysis were consistent with this.Response to antidepressants is greater in RCTs than in observational studies. Observational studies should be considered as a necessary complement to RCTs