Non-parametric estimation of mixed discrete choice models

In this paper, different strands of literature are combined in order to obtain algorithms for semi-parametric estimation of discrete choice models that include the modelling of unobserved heterogeneity by using mixing distributions for the parameters defining the preferences. The models use the theory on non-parametric maximum likelihood estimation (NP-MLE) that has been developed for general mixing models. The expectation-maximization (EM) techniques used in the NP-MLE literature are combined with strategies for choosing appropriate approximating models using adaptive grid techniques. \\ Jointly this leads to techniques for specification and estimation that can be used to obtain a consistent specification of the mixing distribution. Additionally, also algorithms for the estimation are developed that help to decrease problems due to the curse of dimensionality. \\ The proposed algorithms are demonstrated in a small scale simulation study to be useful for the specification and estimation of mixture models in the discrete choice context providing some information on the specification of the mixing distribution. The simulations document that some aspects of the mixing distribution such as the expectation can be estimated reliably. They also demonstrate, however, that typically different approximations to the mixing distribution lead to similar values of the likelihood and hence are hard to discriminate. Therefore it does not appear to be possible to reliably infer the most appropriate parametric form for the estimated mixing distribution.Comment: Paper presented at the International Choice Modelling Conference (ICMC2019) in Kobe, Japa

Hochpräzisionsgrößenmessung und Bestimmung der Topologie subchromosomaler Domänen nach molekularer Markierung unter Berücksichtigung des Einflusses der Zellfixierung

Lichtoptische Untersuchungen der dynamischen Zellkernarchitektur in vivo benötigen zum jetzigen Zeitpunkt aufwendige Markierungs- und Detektionstechniken. Für einige Fragestellungen, wie zum Beispiel die Größe und Lage von Genen, sind Messungen in fixierten Präparaten sinnvoll. In dieser Arbeit wurde der Einfluss der Fixierung auf die Morphologie von Zellkernen sowie auf die Größe und Position subchromosomaler Domänen im Zellkern quantitativ untersucht. Die Quantifizierung der Größen als laterale Ausdehnung erfolgte mittels dem multi point model. Die Morphologie der Zellkerne wird durch die Art der Fixierung und die Hybridisierung nicht einheitlich beeinflusst. Die laterale Ausdehnung der untersuchten Domänen unterscheidet sich nur gering zwischen den Fixierungen. Eine unterschiedliche Sensitivität innerhalb mitotischer Chromosomen gegenüber denaturierenden Prozessen konnte ebenfalls quantifiziert werden

Expression site attenuation mechanistically links antigenic variation and development in Trypanosoma brucei

We have discovered a new mechanism of monoallelic gene expression that links antigenic variation, cell cycle, and development in the model parasite Trypanosoma brucei. African trypanosomes possess hundreds of variant surface glycoprotein (VSG) genes, but only one is expressed from a telomeric expression site (ES) at any given time. We found that the expression of a second VSG alone is sufficient to silence the active VSG gene and directionally attenuate the ES by disruptor of telomeric silencing-1B (DOT1B)-mediated histone methylation. Three conserved expression-site-associated genes (ESAGs) appear to serve as signal for ES attenuation. Their depletion causes G1-phase dormancy and reversible initiation of the slender-to-stumpy differentiation pathway. ES-attenuated slender bloodstream trypanosomes gain full developmental competence for transformation to the tsetse fly stage. This surprising connection between antigenic variation and developmental progression provides an unexpected point of attack against the deadly sleeping sickness

Out-of-hospital births: A small but growing phenomenon in high income countries: A viewpoint.

This short viewpoint article raises some interesting points about freebirthing or unassisted childbirth as a growing phenomenon in high-income countrie

Out-of-hospital births: A small but growing phenomenon in high income countries: A viewpoint

This is the final version. Available on open access from the South Asian Midwifery Alliance via the link in this recor

How to create coats for all seasons: elucidating antigenic variation in African trypanosomes

Extracellular parasites of the mammalian bloodstream face considerable challenges including incessant assault by the immune system. African trypanosomes are consummate survivors in this inclement environment and are renowned for their supremely sophisticated strategy of antigenic variation of their protective surface coat during the course of chronic infections. Recent developments are making us realize how complex this antigenic machinery is and are allowing us to tackle previously intractable problems. However, many of the simplest (and arguably the most important) questions still remain unanswered