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Checklist for the qualitative evaluation of clinical studies with particular focus on external validity and model validity
Gudrun Bornh?ft, Stefanie Maxion-Bergemann, Ursula Wolf, Gunver S Kienle, Andreas Michalsen, Horst C Vollmar, Simon Gilbertson, Peter F Matthiessen
BMC Medical Research Methodology , 2006, DOI: 10.1186/1471-2288-6-56
Abstract: The checklist was developed by listing the most commonly used assessment criteria for clinical studies. Additionally, specific lists for individual applications were included. The categories of biases of internal validity (selection, performance, attrition and detection bias) correspond to structural, treatment-related and observational differences between the test and control groups. Analogously, we have extended these categories to address external validity and model validity, regarding similarity between the study population/conditions and the general population/conditions related to structure, treatment and observation.A checklist is presented, in which the evaluation criteria concerning external validity and model validity are systemised and transformed into a questionnaire format.The checklist presented in this article can be applied to both planning and evaluating of clinical studies. We encourage the prospective user to modify the checklists according to the respective application and research question. The higher expenditure needed for the evaluation of clinical studies in systematic reviews is justified, particularly in the light of the influential nature of their conclusions on therapeutic decisions and the creation of clinical guidelines.It is known that clinical studies can generate discordant results. This observation is addressed scientifically in various ways. Deviant study results may be understood as an expression of spreading or scattering from a supposed true value (whereas deviation depends on the precision of the methods). An alternative approach is to explain differences not statistically but by way of content [1]. In considering individual studies, there should be an estimate to what extent the study conclusions are distorted by systematic factors of bias. Here the focus lies usually on so called internal validity, the comparability of test and control groups. (Detailed definitions of internal validity and other validity categories are given
Antidepressiva in der Schwangerschaft
Bergemann N
Speculum - Zeitschrift für Gyn?kologie und Geburtshilfe , 2009,
Antidepressiva in der Schwangerschaft
Bergemann N
Journal für Neurologie, Neurochirurgie und Psychiatrie , 2009,
Abstract: Nicht nur im Wochenbett, sondern bereits in der Schwangerschaft kommt es h ufig zu depressiven St rungen. Die Erkrankungsrate im zweiten und dritten Trimenon liegt einer neueren Metaanalyse zufolge bei etwa 12,8 bzw. 12,0 %. Dies macht nicht selten eine medikament se Behandlung mit Antidepressiva in der Schwangerschaft erforderlich. Die hier gegebene übersicht zeigt, dass zahlreiche Antidepressiva auch in der Schwangerschaft mit relativ geringem Risiko eingesetzt werden k nnen. Allerdings ist die Verordnung von Antidepressiva immer eine individuelle Risiko-Nutzen- Abw gung zwischen der m glichen Gef hrdung des Kindes durch reproduktions- oder fetotoxische Medikamenteneigenschaften und der Gef hrdung von Mutter und Kind durch Nichtbehandlung einer depressiven Erkrankung, die auch mit Suizidalit t und Mangelern hrung einhergehen kann.
NLTE abundances of Cr in the Sun and metal-poor stars
Maria Bergemann
Physics , 2010,
Abstract: We investigate statistical equilibrium of Cr in the atmospheres of late-type stars. The main goal is to ascertain the reason for a systematic abundance discrepancy between Cr I and Cr II lines, which is often encountered in spectroscopic analyses of metal-poor stars. Up to now, all these studies relied on the assumption of local thermodynamic equilibrium (LTE) in the spectrum modelling. For the first time, we perform NLTE calculations in subdwarfs and subgiants of different metallicities. We show that the LTE assumption is inadequate to describe excitation-ionization equilibrium of Cr I/Cr II in stellar atmospheres and, as a result, leads to large errors in abundances. In particular, the NLTE abundance corrections to Cr I lines range from $+0.3$ to $+0.5$ dex at low [Fe/H]. The NLTE [Cr/Fe] trend in the halo and the disk is flat and can be reproduced by most of the models of Galactic chemical evolution with standard prescriptions for Cr and Fe nucleosynthesis.
Analysis of stellar spectra with 3D and NLTE models
Maria Bergemann
Physics , 2014,
Abstract: Models of radiation transport in stellar atmospheres are the hinge of modern astrophysics. Our knowledge of stars, stellar populations, and galaxies is only as good as the theoretical models, which are used for the interpretation of their observed spectra, photometric magnitudes, and spectral energy distributions. I describe recent advances in the field of stellar atmosphere modelling for late-type stars. Various aspects of radiation transport with 1D hydrostatic, LTE, NLTE, and 3D radiative-hydrodynamical models are briefly reviewed.
Ionization balance of Ti in the photospheres of the Sun and four late-type stars
Maria Bergemann
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.18295.x
Abstract: In this paper we investigate statistical equilibrium of Ti in the atmospheres of late-type stars. The Ti I/Ti II level populations are computed with available experimental atomic data, except for photoionization and collision induced transition rates, for which we have to rely on theoretical approximations. For the Sun, the NLTE line formation with adjusted H I inelastic collision rates and MAFAGS-OS model atmosphere solve the long-standing discrepancy between Ti I and Ti II lines. The NLTE abundances determined from both ionization stages agree within $0.01$ dex with each other and with the Ti abundance in C I meteorites. The Ti NLTE model does not perform similarly well for the metal-poor stars, overestimating NLTE effects in the atmospheres of dwarfs, but underestimating overionization for giants. Investigating different sources of errors, we find that only [Ti/Fe] ratios based on Ti II and Fe II lines can be safely used in studies of Galactic chemical evolution. To avoid spurious abundance trends with metallicity and dwarf/giant discrepancies, it is strongly recommended to disregard Ti I lines in abundance analyses, as well as in determination of surface gravities.
Role of input atomic data in spectroscopic analyses of the Sun and metal-poor stars
Maria Bergemann
Physics , 2011,
Abstract: Analysis of high-resolution stellar spectra relies heavily upon atomic data. These include energy levels, wavelengths, cross-sections for various types of interactions between particles and photons, such as photoionization and collision induced transitions. Quantum-mechanical calculations provide largest part of these data. In this paper I describe atomic data necessary to compute model atmospheres and line formation for the late-type stars both in the assumption of local thermodynamic equilibrium (LTE) and in a more general case of non-LTE. I will focus on transition metals with 21 < Z < 29 and discuss whether (and where) more complete and/or accurate atomic data are necessary.
Signótica , 2000, DOI: 10.5216/sig.v13i1.7297
Abstract: Este trabalho tem por objetivo analisar três ensaios sobre o romance francês Os miseráveis, de Victor Hugo, a que leitores brasileiros do século XIX tiveram acesso. Ressalta-se como a crítica literária da época contemplava de forma generosa o plano do conteúdo, em detrimento do domínio do discurso e suas condi es de produ o. Ce texte examine trois essais sur le roman fran ais Les misérables (1862), de Victor Hugo, lus par les Brésiliens du XIXe siècle. On observe l’importance que la critique littéraire de cette époque accordait à l’analyse du contenu au détriment de l’étude du discours et des conditions de sa production.
Chromium: NLTE abundances in metal-poor stars and nucleosynthesis in the Galaxy
Maria Bergemann,Gabriele Cescutti
Physics , 2010, DOI: 10.1051/0004-6361/201014250
Abstract: Aims. We investigate statistical equilibrium of Cr in the atmospheres of late-type stars to show whether the systematic abundance discrepancy between Cr I and Cr II lines, as often encountered in the literature, is due to deviations from LTE. Furthermore, we attempt to interpret the NLTE trend of [Cr/Fe] with [Fe/H] using chemical evolution models for the solar neighborhood. Methods. NLTE calculations are performed for the model of Cr atom, comprising 340 levels and 6806 transitions in total. We make use of the quantum-mechanical photoionization cross-sections of Nahar (2009) and investigate sensitivity of the model to uncertain cross-sections for H I collisions. NLTE line formation is performed for the MAFAGS-ODF model atmospheres of the Sun and 10 metal-poor stars with -3.2 < [Fe/H] < -0.5, and abundances of Cr are derived by comparison of the synthetic and observed flux spectra. Results. We achieve good ionization equilibrium of Cr for the models with different stellar parameters, if inelastic collisions with H I atoms are neglected. The solar NLTE abundance based on Cr I lines is 5.74 dex with {\sigma} = 0.05 dex; it is \sim 0.1 higher than the LTE abundance. For the metal-poor stars, the NLTE abundance corrections to Cr I lines range from +0.3 to +0.5 dex. The resulting [Cr/Fe] ratio is roughly solar for the range of metallicities analyzed here, which is consistent with current views on production of these iron peak elements in supernovae. Conclusions. The tendency of Cr to become deficient with respect to Fe in metal-poor stars is an artifact due to neglect of NLTE effects in the line formation of Cr I, and it has no relation to peculiar physical conditions in the Galactic ISM or deficiencies of nucleosynthesis theory.
Fe-peak element abundances in disk and halo stars
Maria Bergemann,Thomas Gehren
Physics , 2009, DOI: 10.1017/S1743921310000864
Abstract: At present none of Galactic chemical evolution (GCE) models provides a self-consistent description of observed trends for all iron-peak elements with metallicity simultaneously. The question is whether the discrepancy is due to deficiencies of GCE models, such as stellar yields, or due to erroneous spectroscopically-determined abundances of these elements in metal-poor stars. The present work aims at a critical reevaluation of the abundance trends for several odd and even-Z Fe-peak elements, which are important for understanding explosive nucleosynthesis in supernovae.
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