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Statistical matching offers a way to broaden the scope of analysis without increasing respondent burden and costs. These would result from conducting a new survey or adding variables to an existing one. Statistical matching aims at combining two datasets A and B referring to the same target population in order to analyse variables, say Y and Z, together, that initially were not jointly observed. The matching is performed based on matching variables X that correspond to common variables present in both datasets A and B. Furthermore, Y is only observed in B and Z is only observed in A. To overcome the fact that no joint information on X, Y and Z is available, statistical matching procedures have to rely on suitable assumptions. Therefore, to yield a theoretical foundation for statistical matching, most procedures rely on the conditional independence assumption (CIA), i.e. given X, Y is independent of Z.
The goal of this thesis is to encompass both the statistical matching process and the analysis of the matched dataset. More specifically, the aim is to estimate a linear regression model for Z given Y and possibly other covariates in data A. Since the validity of the assumptions underlying the matching process determine the validity of the obtained matched file, the accuracy of statistical inference is determined by the suitability of the assumptions. By putting the focus on these assumptions, this work proposes a systematic categorisation of approaches to statistical matching by relying on graphical representations in form of directed acyclic graphs. These graphs are particularly useful in representing dependencies and independencies which are at the heart of the statistical matching problem. The proposed categorisation distinguishes between (a) joint modelling of the matching and the analysis (integrated approach), and (b) matching subsequently followed by statistical analysis of the matched dataset (classical approach). Whereas the classical approach relies on the CIA, implementations of the integrated approach are only valid if they converge, i.e. if the specified models are identifiable and, in the case of MCMC implementations, if the algorithm converges to a proper distribution.
In this thesis an implementation of the integrated approach is proposed, where the imputation step and the estimation step are jointly modelled through a fully Bayesian MCMC estimation. It is based on a linear regression model for Z given Y and accounts for both a linear regression model and a random effects model for Y. Furthermore, it yields its validity when the instrumental variable assumption (IVA) holds. The IVA corresponds to: (a) Z is independent of a subset X’ of X given Y and X*, where X* = X\X’ and (b) Y is correlated with X’ given X*. The proof, that the joint Bayesian modelling of both the model for Z and the model for Y through an MCMC simulation converges to a proper distribution is provided in this thesis. In a first model-based simulation study, the proposed integrated Bayesian procedure is assessed with regard to the data situation, convergence issues, and underlying assumptions. Special interest lies in the investigation of the interplay of the Y and the Z model within the imputation process. It turns out that failure scenarios can be distinguished by comparing the CIA and the IVA in the completely observed dataset.
Finally, both approaches to statistical matching, i.e. the classical approach and the integrated approach, are subject to an extensive comparison in (1) a model-based simulation study and (2) a simulation study based on the AMELIA dataset, which is an openly available very large synthetic dataset and, by construction, similar to the EU-SILC survey. As an additional integrated approach, a Bayesian additive regression trees (BART) model is considered for modelling Y. These integrated procedures are compared to the classical approach represented by predictive mean matching in the form of multiple imputations by chained equation. Suitably chosen, the first simulation framework offers the possibility to clarify aspects related to the underlying assumptions by comparing the IVA and the CIA and by evaluating the impact of the matching variables. Thus, within this simulation study two related aspects are of special interest: the assumptions underlying each method and the incorporation of additional matching variables. The simulation on the AMELIA dataset offers a close-to-reality framework with the advantage of knowing the whole setting, i.e. the whole data X, Y and Z. Special interest lies in investigating assumptions through adding and excluding auxiliary variables in order to enhance conditional independence and assess the sensitivity of the methods to this issue. Furthermore, the benefit of having an overlap of units in data A and B for which information on X, Y, Z is available is investigated. It turns out that the integrated approach yields better results than the classical approach when the CIA clearly does not hold. Moreover, even when the classical approach obtains unbiased results for the regression coefficient of Y in the model for Z, it is the method relying on BART that over all coefficients performs best.
Concluding, this work constitutes a major contribution to the clarification of assumptions essential to any statistical matching procedure. By introducing graphical models to identify existing approaches to statistical matching combined with the subsequent analysis of the matched dataset, it offers an extensive overview, categorisation and extension of theory and application. Furthermore, in a setting where none of the assumptions are testable (since X, Y and Z are not observed together), the integrated approach is a valuable asset by offering an alternative to the CIA.
A model-based temperature adjustment scheme for wintertime sea-ice production retrievals from MODIS
(2022)
Knowledge of the wintertime sea-ice production in Arctic polynyas is an important requirement for estimations of the dense water formation, which drives vertical mixing in the upper ocean. Satellite-based techniques incorporating relatively high resolution thermal-infrared data from MODIS in combination with atmospheric reanalysis data have proven to be a strong tool to monitor large and regularly forming polynyas and to resolve narrow thin-ice areas (i.e., leads) along the shelf-breaks and across the entire Arctic Ocean. However, the selection of the atmospheric data sets has a large influence on derived polynya characteristics due to their impact on the calculation of the heat loss to the atmosphere, which is determined by the local thin-ice thickness. In order to overcome this methodical ambiguity, we present a MODIS-assisted temperature adjustment (MATA) algorithm that yields corrections of the 2 m air temperature and hence decreases differences between the atmospheric input data sets. The adjustment algorithm is based on atmospheric model simulations. We focus on the Laptev Sea region for detailed case studies on the developed algorithm and present time series of polynya characteristics in the winter season 2019/2020. It shows that the application of the empirically derived correction decreases the difference between different utilized atmospheric products significantly from 49% to 23%. Additional filter strategies are applied that aim at increasing the capability to include leads in the quasi-daily and persistence-filtered thin-ice thickness composites. More generally, the winter of 2019/2020 features high polynya activity in the eastern Arctic and less activity in the Canadian Arctic Archipelago, presumably as a result of the particularly strong polar vortex in early 2020.
The larval stage of the European fire salamander (Salamandra salamandra) inhabits both lentic and lotic habitats. In the latter, they are constantly exposed to unidirectional water flow, which has been shown to cause downstream drift in a variety of taxa. In this study, a closed artificial creek, which allowed us to keep the water flow constant over time and, at the same time, to simulates with predefined water quantities and durations, was used to examine the individual movement patterns of marked larval fire salamanders exposed to unidirectional flow. Movements were tracked by marking the larvae with VIAlpha tags individually and by using downstream and upstream traps. Most individuals showed stationarity, while downstream drift dominated the overall movement pattern. Upstream movements were rare and occurred only on small distances of about 30 cm; downstream drift distances exceeded 10 m (until next downstream trap). The simulated flood events increased drift rates significantly, even several days after the flood simulation experiments. Drift probability increased with decreasing body size and decreasing nutritional status. Our results support the production hypothesis as an explanation for the movements of European fire salamander larvae within creeks.
Measurements of the atmospheric boundary layer (ABL) structure were performed for three years (October 2017–August 2020) at the Russian observatory “Ice Base Cape Baranova” (79.280° N, 101.620° E) using SODAR (Sound Detection And Ranging). These measurements were part of the YOPP (Year of Polar Prediction) project “Boundary layer measurements in the high Arctic” (CATS_BL) within the scope of a joint German–Russian project. In addition to SODAR-derived vertical profiles of wind speed and direction, a suite of complementary measurements at the observatory was available. ABL measurements were used for verification of the regional climate model COSMO-CLM (CCLM) with a 5 km resolution for 2017–2020. The CCLM was run with nesting in ERA5 data in a forecast mode for the measurement period. SODAR measurements were mostly limited to wind speeds <12 m/s since the signal was often lost for higher winds. The SODAR data showed a topographical channeling effect for the wind field in the lowest 100 m and some low-level jets (LLJs). The verification of the CCLM with near-surface data of the observatory showed good agreement for the wind and a negative bias for the 2 m temperature. The comparison with SODAR data showed a positive bias for the wind speed of about 1 m/s below 100 m, which increased to 1.5 m/s for higher levels. In contrast to the SODAR data, the CCLM data showed the frequent presence of LLJs associated with the topographic channeling in Shokalsky Strait. Although SODAR wind profiles are limited in range and have a lot of gaps, they represent a valuable data set for model verification. However, a full picture of the ABL structure and the climatology of channeling events could be obtained only with the model data. The climatological evaluation showed that the wind field at Cape Baranova was not only influenced by direct topographic channeling under conditions of southerly winds through the Shokalsky Strait but also by channeling through a mountain gap for westerly winds. LLJs were detected in 37% of all profiles and most LLJs were associated with channeling, particularly LLJs with a jet speed ≥ 15 m/s (which were 29% of all LLJs). The analysis of the simulated 10 m wind field showed that the 99%-tile of the wind speed reached 18 m/s and clearly showed a dipole structure of channeled wind at both exits of Shokalsky Strait. The climatology of channeling events showed that this dipole structure was caused by the frequent occurrence of channeling at both exits. Channeling events lasting at least 12 h occurred on about 62 days per year at both exits of Shokalsky Strait.
Algorithmen als Richter
(2022)
Die menschliche Entscheidungsgewalt wird durch algorithmische
Entscheidungssysteme herausgefordert. Verfassungsrechtlich besonders
problematisch ist dies in Bereichen, die das staatliche Handeln betreffen.
Eine herausgehobene Stellung nimmt durch den besonderen Schutz der
Art. 92 ff. GG die rechtsprechende Gewalt ein. Lydia Wolff fragt daher danach, welche Antworten das Grundgesetz auf digitale Veränderungen in diesem Bereich bereithält und wie sich ein Eigenwert menschlicher Entscheidungen in der Rechtsprechung angesichts technischen Wandels darstellen lässt.
Das Werk erörtert hierzu einen Beitrag zum verfassungsrechtlichen
Richterbegriff und stellt diesen etablierten Begriff in einen Kontext neuer digitaler Herausforderungen durch algorithmische Konkurrenz.
The paper aims to recognize the changes in the barriers to cross-border educational projects, especially in the context of the COVID-19 pandemic. The research focused on the European borderlands, where the level of maturity of cross-border cooperation is diverse (the Franco-German and Polish-Czech bor-derlands). The author utilised qualitative research methods (desk research, in-depth interview, case study). An exploratory study covered the barriers existing before the pandemic that stayed stable or have changed during the pandemic, and the new types of barriers that have appeared then. Within both borderlands, the identified barriers were similar in general; however, their intensity was varied. The key difference was the approach to these barriers within each borderland. On the Franco-German border, cross-border cooperation is more complex and deeper, and on the Polish-Czech border, it is more su-perficial and focused on specific issues only. These differences reveal the solutions that should be im-plemented to mitigate the impact of the pandemic on those projects within each borderland.
Insekten stellen die artenreichste Klasse des Tierreichs dar, wobei viele der Arten bedroht sind. Das liegt neben dem Klimawandel vor allem an der sich in den letzten Jahrzehnten stark verändernden landwirtschaftlichen Nutzung von Flächen, was zu Lebensraumzerstörung und Habitatfragmentierung führt. Die intensivere Bewirtschaftung von Gunstflächen einerseits, sowie die Flächenaufgabe unrentabler Flächen andererseits, hat schwerwiegende Folgen für Insekten, die an extensiv genutzte Kulturflächen angepasst sind, was besonders durch den abnehmenden Anteil an Spezialisten deutlich wird. Eine Region, die aufgrund des kleinräumigen Nebeneinanders von naturnahen Bereichen und anthropogen geschaffenen Kulturflächen (entlang eines großen Höhengradienten) eine wichtige Rolle für die Biodiversität besitzt, speziell als Lebensraum für Spezialisten aller Artengruppen, sind die Alpen. Auch hier stellt der landwirtschaftliche Nutzungswandel ein großes Problem dar, weshalb es einen nachhaltigen Schutz der extensiv genutzten Kulturlebensräume bedarf. Um zu klären, wie eine nachhaltige Berglandwirtschaft zukünftig erhalten bleiben kann, wurden im ersten Kapitel der Promotion die Regelungsrahmen der internationalen, europäischen, nationalen und regionalen Gesetze näher betrachtet. Es zeigt sich, dass der multifunktionale Ansatz der Alpenkonvention und des zugehörigen Protokolls „Berglandwirtschaft“ nur eine geringe normative Konkretisierung aufweisen und daher nicht im ausreichenden Maße in der Gemeinsamen Agrarpolitik der EU sowie im nationalen Recht umgesetzt werden; dadurch können diese einer negativen Entwicklung in der Berglandwirtschaft nicht ausreichend entgegenwirken. Neben diesen Rechtsgrundlagen fehlt es jedoch auch an naturwissenschaftlichen Grundlagen, um die Auswirkungen des landwirtschaftlichen Nutzungswandels auf alpine und arktische Tierarten zu beurteilen. Untersuchungen mit Charakterarten für diese Kulturräume sind somit erforderlich, wobei Tagfalter aufgrund ihrer Sensibilität gegenüber Umweltveränderungen geeignete Indikatoren sind. Deshalb wurden im zweiten Kapitel der Promotion die beiden Schwestertaxa Boloria pales und B. napaea untersucht, die für arktische und / oder alpine Grünlandflächen typisch sind. Die bisher unbekannte Phylogeographie beider Arten wurde daher mit zwei mitochondrialen und zwei Kerngenen über das gesamte europäische Verbreitungsgebiet untersucht. In diesem Zusammenhang die zwischen- und innerartlichen Auftrennungen analysiert und datiert sowie die ihnen unterliegenden Ausbreitungsmuster entschlüsselt. Um spezielle Anpassungsformen an die arktischen und alpinen Lebensräume der Arten zu entschlüsseln und die Folgen der landwirtschaftlichen Nutzungsänderung richtig einordnen zu können, wurden mehrere Populationen beider Arten freilandökologisch untersucht. Während B. pales über den gesamten alpinen Sommer schlüpfen kann und proterandrische Strukturen zeigt, ist B. napaea durch das Fehlen der Proterandie und ein verkürztes Schlupfzeitfenster eher an die kürzeren, arktischen Sommer angepasst. Obwohl beide Arten die gleichen Nektarquellen nutzen, gibt es aufgrund verschiedener Bedürfnisse Unterschiede in den Nektarpräferenzen zwischen den Geschlechtern; auch innerartliche Unterschiede im Dispersionsverhalten wurden gefunden. Populationen beider Arten können eine kurze Beweidung überleben, wobei der Zeitpunkt der Beweidung von Bedeutung ist; eine Nutzung gegen Ende der Schlupfphase hat einen größeren Einfluss auf die Population. Daneben wurde ein deutlicher Unterschied zwischen Flächen mit langfristiger und fehlender Beweidung gefunden. Neben einer geringen Populationsdichte, gibt es auf ganzjährig beweideten Flächen einen größeren Druck, den Lebensraum zu verlassen und die zurückgelegten Flugdistanzen sind hier auch deutlich größer.
Die endemischen Arganbestände in Südmarokko sind die Quelle des wertvollen Arganöls, sind aber durch bspw. Überweidung oder illegale Feuerholzgewinnung stark übernutzt. Aufforstungsmaßnahmen sind vorhanden, sind aber aufgrund von zu kurz angelegten Bewässerungs- und Schutzverträgen häufig nicht erfolgreich. Das Aufkommen von Neuwuchs ist durch das beinahe restlose Sammeln von Kernen kaum möglich, durch Fällen oder Absterben von Bäumen verringert sich die kronenüberdeckte Fläche und unbedeckte Flächen zwischen den Bäumen nehmen zu.
Die Entwicklung der Arganbestände wurde über den Zeitraum von 1972 und 2018 mit historischen und aktuellen Satellitenbildern untersucht, ein Großteil der Bäume hat sich in dieser Zeit kaum verändert. Zustandsaufnahmen von 2018 zeigten, dass viele dieser Bäume durch Überweidung und Abholzung nur als Sträucher wachsen und so in degradiertem Zustand stabil sind.
Trotz der Degradierung einiger Bäume zeigt sich, dass der Boden unter den Bäumen die höchsten Gehalte an organischer Bodensubstanz und Nährstoffen auf den Flächen aufweist, zwischen zwei Bäumen sind die Gehalte am niedrigsten. Der Einfluss des Baumes auf den Boden geht über die Krone hinaus in Richtung Norden durch Beschattung in der Mittagssonne, Osten durch Windverwehung von Streu und Bodenpartikeln und hangabwärts durch Verspülung von Material.
Über experimentelle Methoden unter und zwischen den Arganbäumen wurden Erkenntnisse zur Bodenerosion gewonnen. Die hydraulische Leitfähigkeit unter Bäumen ist um den Faktor 1,2-1,5 höher als zwischen den Bäumen, Oberflächenabflüsse und Bodenabträge sind unter den Bäumen etwas niedriger, bei degradierten Bäumen ähnlich den Bereichen zwischen den Bäumen. Die unterschiedlichen Flächenbeschaffenheiten wurden mit einem Windkanal untersucht und zeigten, dass gerade frisch gepflügte Flächen hohe Windemissionen verursachen, während Flächen mit hoher Steinbedeckung kaum von Winderosion betroffen sind.
Die Oberflächenabflüsse von den unterschiedlichen Flächentypen werden in die Vorfluter abgeleitet. Die Sedimentdynamik in diesen Wadis wird hauptsächlich von Niederschlag zwischen den Messungen, Einzugsgebiet und Wadilänge und kaum von den verschiedenen Landnutzungen beeinflusst.
Das Landschaftssystem Argan konnte über diesen Multi-Methodenansatz auf verschiedenen Ebenen analysiert werden.
List-method directed forgetting (LMDF) is the demonstration that people can intentionally forget previously studied information when they are asked to forget what they have previously learned and remember new information instead. In addition, recent research demonstrated that people can selectively forget when cued to forget only a subset of the previously studied information. Both forms of forgetting are typically observed in recall tests, in which the to-be-forgotten and to-be-remembered information is tested independent of original cuing. Thereby, both LMDF and selective directed forgetting (SDF) have been studied mostly with unrelated item materials (e.g., word lists). The present study examined whether LMDF and SDF generalize to prose material. Participants learned three prose passages, which they were cued to remember or forget after the study of each passage. At the time of testing, participants were asked to recall the three prose passages regardless of original cuing. The results showed no significant differences in recall of the three lists as a function of cuing condition. The findings suggest that LMDF and SDF do not occur with prose material. Future research is needed to replicate and extend these findings with (other) complex and meaningful materials before drawing firm conclusions. If the null effect proves to be robust, this would have implications regarding the ecological validity and generalizability of current LMDF and SDF findings.