Dissertations / Theses on the topic 'Confounding Factor'
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Tarassova, Olga. "Effects of physical and cognitive exercise on levels of peripheral BDNF in elderly : with cardiorespiratory fitness as a potential confounding factor." Thesis, Gymnastik- och idrottshögskolan, GIH, Institutionen för idrotts- och hälsovetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:gih:diva-5850.
Zayat, Ahmed Salem. "Confounding factors in musculoskeletal ultrasound." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.574628.
Redman, Mary W. "Estimating causal effects with observational data : the intensity-score approach to adjusting for confounding /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/9596.
Taylor, Jean. "Birth weight and acute childhood leukemia : a meta-analysis of observational studies /." Download the dissertation in PDF, 2005. http://www.lrc.usuhs.mil/dissertations/pdf/Taylor2005.pdf.
Bernhardt, Alexandra A. "Saliva cortisol profiles in field research internal structure, confounding factors, quantification, and stability." [S.l. : s.n.], 2007. http://nbn-resolving.de/urn:nbn:de:bsz:180-madoc-13928.
Zielke, Hanno [Verfasser]. "Time-related alterations and other confounding factors in direct sediment contact tests / Hanno Zielke." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2011. http://d-nb.info/1014298180/34.
Ylöstalo, P. (Pekka). "Dental health, lifestyle and cardiovascular risk factors—a study among a cohort of young adult population in northern Finland." Doctoral thesis, University of Oulu, 2008. http://urn.fi/urn:isbn:9789514287213.
Tarafder, Mushfiqur R. "Effect of measurement error in the estimation of prevalence of infection and epidemiological associations for helminths." Oklahoma City : [s.n.], 2009.
Pressat-Laffouilhère, Thibaut. "Modèle ontologique formel, un appui à la sélection des variables pour la construction des modèles multivariés." Electronic Thesis or Diss., Normandie, 2023. http://www.theses.fr/2023NORMR104.
Responding to a causal research question in the context of observational studies requires the selection ofconfounding variables. Integrating them into a multivariate model as co-variables helps reduce bias in estimatingthe true causal effect of exposure on the outcome. Identification is achieved through causal diagrams (CDs) ordirected acyclic graphs (DAGs). These representations, composed of nodes and directed arcs, prevent theselection of variables that would introduce bias, such as mediating and colliding variables. However, existingmethods for constructing CDs lack systematic approaches and exhibit limitations in terms of formalism,expressiveness, and completeness. To offer a formal and comprehensive framework capable of representing allnecessary information for variable selection on an enriched CD, analyzing this CD, and, most importantly,explaining the analysis results, we propose utilizing an ontological model enriched with inference rules. Anontological model allows for representing knowledge in the form of an expressive and formal graph consisting ofclasses and relations similar to the nodes and arcs of Cds. We developed the OntoBioStat (OBS) ontology basedon a list of competency questions about variable selection and an analysis of scientific literature on CDs andontologies. The construction framework of OBS is richer than that of a CD, incorporating implicit elements likenecessary causes, study context, uncertainty in knowledge, and data quality. To evaluate the contribution of OBS,we used it to represent variables from a published observational study and compared its conclusions with thoseof a CD. OBS identified new confounding variables due to its different construction framework and the axiomsand inference rules. OBS was also used to represent an ongoing retrospective study analysis. The modelexplained statistical correlations found between study variables and highlighted potential confounding variablesand their possible substitutes (proxies). Information on data quality and causal relation uncertainty facilitatedproposing sensitivity analyses, enhancing the study's conclusion robustness. Finally, inferences were explainedthrough the reasoning capabilities provided by OBS's formal representation. Ultimately, OBS will be integratedinto statistical analysis tools to leverage existing libraries for variable selection, making it accessible toepidemiologists and biostatisticians
Eklundh, Thomas. "Lumbar puncture in psychiatric research : on the impact of confounding factors on monoamine compounds in cerebrospinal fluid /." Stockholm, 2000. http://diss.kib.ki.se/2000/91-628-4490-3/.
Bernhardt, Alexandra A. [Verfasser]. "Saliva cortisol profiles in field research : internal structure, confounding factors, quantification, and stability / vorgelegt von Alexandra A. Bernhardt." [Mannheim] : [Univ.], 2007. http://d-nb.info/992375185/34.
Ivanova, Maria V. "Addressing Confounding Factors in the Study of Working Memory in Aphasia: Empirical Evaluation of Modified Tasks and Measures." View abstract, 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3371473.
Murphy, Gary. "Serological methods for monitoring HIV transmission trends : Investigation of confounding factors and improved estimation of HIV incidence in target populations." Thesis, Queen Mary, University of London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504542.
Corley, Janie Elizabeth. "Lifestyle factors and cognitive ageing in the Lothian Birth Cohort 1936 : exploring the role of confounding by prior cognitive ability." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/20984.
Bergvall, Niklas. "Fetal programming and subsequent risks in adulthood: are the associations confounded by genetic and/or environmental factors? /." Stockholm : Department of Medical Epidemiology and Biostatistics, Karolinska institutet, 2007. http://diss.kib.ki.se/2007/978-91-7357-271-2/.
Wennberg, Maria, Andreas Tornevi, Ingegerd Johansson, Agneta Hörnell, Margareta Norberg, and Ingvar A. Bergdahl. "Diet and lifestyle factors associated with fish consumption in men and women : a study of whether gender differences can result in gender-specific confounding." Umeå universitet, Yrkes- och miljömedicin, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-62237.
Hamilton, Mark. "Why Do I Live For The Moment? The Effects of Genetic Factors and Adverse Childhood Experiences on Cognitive Traits in Middle Adulthood." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1563873193728586.
Khati, Makobetsa. "An analysis of alcohol use and possible confounding risk factors for risky sexual behaviour amongst women in the rural Western Cape and urban Gauteng provinces." Master's thesis, University of Cape Town, 2013. http://hdl.handle.net/11427/11004.
Includes bibliographical references.
The general aim of this thesis is therefore to analyse alcohol consumption variables and possible confounding risk factors associated with risky sexual behaviour amongst women in the urban city of Tshwane in Gauteng and the rural Western Cape sites, respectively.
Le, Borgne Florent. "Conception d’un outil simple d'utilisation pour réaliser des analyses statistiques ajustées valorisant les données de cohortes observationnelles de pathologies chroniques : application à la cohorte DIVAT." Thesis, Nantes, 2016. http://www.theses.fr/2016NANT1003/document.
In medical research, cohorts help to better understandthe evolution of a pathology and improve the care ofpatients. Causal associations between risk factors andoutcomes are regularly studied through etiological studies. Cohorts analysis also allow the identification of new markers for the prediction of the patient evolution.However, confounding factors are often source of bias in the interpretation of the results of etiologic or prognostic studies.In this manuscript, we presented two research works in Biostatistics, the common topic being propensity scores.In the first work, we compared the performances of different models allowing to evaluate the causality of an exposure on an outcome in the presence of rightc ensored data. In the second work, we proposed anestimator of standardized and weighted time-dependentROC curves. This estimator provides a measure of theprognostic capacities of a marker by taking into accountthe possible confounding factors. Consistent with our objective to provide adapted statistical tools, we also present in this manuscript an application, so-calledPlug-Stat®. Directly linked with the database, it allows toperform statistical analyses adapted to the pathology in order to facilitate epidemiological studies and improve the valorization of data from observational cohorts
Hajage, David. "Utilisation du score de propension et du score pronostique en pharmacoépidémiologie." Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC175/document.
Pharmacoepidemiologic observational studies are often conducted to evaluate newly marketed drugs or drugs in competition with many alternatives. In such cohort studies, the exposure of interest is rare. To take into account confounding factors in such settings, some authors advise against the use of the propensity score in favor of the prognostic score, but this recommendation is not supported by any study especially focused on infrequent exposures and ignores the type of estimation provided by each prognostic score-based method.The first part of this work evaluates the use of propensity score-based methods to estimate the marginal effect of a rare exposure. The second part evaluates the performance of the prognostic score based methods already reported in the literature, compares them with the propensity score based methods, and introduces some new prognostic score-based methods intended to estimate conditional or marginal effects. The last part deals with variance estimators of the treatment effect. We present the opposite consequences of ignoring the estimation step of the propensity score and the prognostic score. We show some new variance estimators accounting for this step
Gismondi, Éric. "Étude des systèmes de défenses antitoxiques chez l'amphipode Gammarus roeseli : effets du parasitisme et d'une exposition au cadmium." Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0050/document.
To cope with environmental disturbances, organisms have developed antitoxic defenses commonly used as biomarkers in environmental risk assessment. However, many confounding factors such as temperature and gender could influence biomarker responses. It seems hence necessary to investigate their effects, in order to attribute biological responses only to pollutants. In this context, we investigated the influence of parasitism by studying the acanthocephalan parasite Polymorphus minutus, horizontally transmitted, and microsporidia parasites, vertically transmitted, on the physiological responses of their common host, the freshwater amphipod Gammarus roeseli, a classical model used in ecotoxicology. We investigated the glutathione, a tripeptide having a key role in antitoxic systems, its synthesis (i.e. gamma-glutamylcysteine ligase activity), energy reserves (i.e. lipids, glycogen, proteins) and a toxicity biomarker, the malondialdehyde. The influence of parasitism was considered in different studies: (i) in G. roeseli infected by P. minutus only, (ii) in G. roeseli infected by microsporidia (mainly Dictyocoela roeselum) and (iii) in G. roeseli coinfected by both parasites. Each study was carried out in absence of pollutants and under cadmium stress. We highlighted that, in the absence of contamination, only P. minutus and the co-infection affect the G. roeseli biomarker assessments. After cadmium exposure, the presence of parasites (i.e. single infection or co-infection) influences the mobilization of antitoxic defences, and accentuates toxic effects in their hosts. Our results underline the confounding nature of parasitism in ecotoxicology and thus, highlight the importance to take into account this parameter in the environmental risk assessment
Caye, Kévin. "Méthodes de factorisation matricielle pour la génomique des populations et les tests d'association." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAS046/document.
We present statistical methods based on matrix factorization problems. A first method allows efficient inference of population structure from genetic data and including geographic proximity information. A second method corrects the association studies for confounding factors. We present in this manuscript the models, as well as the theoretical aspects of the inference algorithms. Moreover, using numerical simulations, we compare the performance of our methods with those of existing methods. Finally, we use our methods on real biological data. Our methods have been implemented and distributed as R packages: tess3r and lfmm
Coulaud, Romain. "Modélisation et changements d'échelles pour l'évaluation écotoxicologique : application à deux macroinvertébrés aquatiques, Gammarus fossarum (crustacé amphipode) et potamopyrgus antipodarum (mollusque gastéropode)." Thesis, Lyon 1, 2012. http://www.theses.fr/2012LYO10018/document.
The regulatory framework lead to increase the assessments of the ecological risk linked to the dischaarge of chemical substances in aquatic environment with the aim to protect natural populations. However, this target level of protection cannot be used so easily to etablish a direcet link between a contamination and its effects. In order to overcome this difficulty, the multi-scale approaches based on the study of the effects of the contaminations on individual markers and then on the extrapolation of these effects at the population level with population dynamic models reprensent promising tools and start to bewell accepted in predictive processes. Yet, their use for the diagnosis of water quality remainsrare for the moment, on the one hand, because of the important varaibility of answers of individual makers in situ linked to the influence of diverse confounding environmental factors for the assessments of toxicity and, on the other hand, because pf the lack of environmental relevance of models currently proposed. Focused on the use of 2 species widely observed in European rivers and presenting contrastingecological and phylogenetic characteristics : the Grammar fossarum crutacean and the Potamopyrgus antipodarum mollusc, this doctoral degree first propose a methodology to consider the influenceof confounding factors in order to improve the reading of biological in situ tests based on the measurment of individual markers on caged organisms and second, to develop ecologically relevant population models. Thus, this work allowed to underline the importance of the consideration of confounding factors (i.e. temperature), in different in situ tests based on the measurment of individul markers on caged organisms. Moreover, population models for both species have been defined in order to test the influence of life histories and seasonal variations on demographic sensitivity of populations
Chen, Yong. "Comparative Effectiveness of Alendronate and Risedronate on the Risk of Non-Vertebral Fractures in Older Women: An Instrumental Variables Approach: A Dissertation." eScholarship@UMMS, 2011. https://escholarship.umassmed.edu/gsbs_diss/582.
Floury, Mathieu. "Analyse des tendances d'évolution de peuplements de macroinvertébrés benthiques dans un contexte de réchauffement des eaux." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2013. http://tel.archives-ouvertes.fr/tel-00844377.
"Projection Properties and Analysis Methods for Six to Fourteen Factor No Confounding Designs in 16 Runs." Doctoral diss., 2012. http://hdl.handle.net/2286/R.I.15895.
Dissertation/Thesis
Ph.D. Industrial Engineering 2012
Rubanzana, Wilson. "Hormonal contraceptives as a risk factor for invasive breast cancer in black women in Johannesburg, South Africa." Thesis, 2008. http://hdl.handle.net/10539/5740.
Ching-Tai, Cheng, and 鄭淨黛. "Analysis of Matzke Method for Vancomycin serum concentration and confounding factors." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/26855203537927898425.
高雄醫學大學
藥學研究所
98
Background The glycopeptide antibiotic vancomycin has been widely used in the treatment of gram-positive infectious diseases; especially those caused by methicillin-resistant Staphylococcus aureus (MRSA). In vancomycin therapy, plasma levels of vancomycin must be monitored to avoid side effects and obtain effective clinical responses in each individual. Several methods have been proposed for setting the initial dosage regimen of vancomycin therapy, including Moellering nomogram, Matzke nomogram and Rodvold etc.. By using the drug monitoring (TDM) data from adult MICU inpatients, this study had evaluated the appropriateness of the Matzke nomogram and tried to find confounding factor that influencing the vancomycin serum concemtration. Methods This is a single-center and retrospective study. All adult patients used vancomycin therapy and with TDM data from July 2004 to June 2009. Data was included in this population model dataset had been included in a previous population modelling study. Demographic data included patient age, gender, total body weight, serum creatinine (Scr) and serum concentrations were collected from TDM files. Creatinine clearance (CLcr) was calculated using the Cockcroft–Gault equation. Vancomycin using less than 48 hours or not using intravenous injection, pregnant or breast-feeding women, burn patients (>10%BSA) and patients on dialysis were excluded from the study. General demographic data with serum concentration and confounding factors were analyzed by linear regression analysis. Results The pharmacokinetics of vancomycin were characterized in 430 patients with different degrees of renal function after an initial dose of 24.8±1.1mg/kg and maintain dose 19.3 ± 1.1 mg/kg. According to the level of CLcr, there were 242, 162 and 26 patients subjects in CLcr > 60 mL/min (group I), 30~60 mL/min (group II) and 10~30 mL/min (group III), respectively. The results showed that peak level 80.2% patients in groups I, 71.6% patients in groups II and 88.5% patients in groups IIII were 20~40 mg/L; the trough level 62.0% patients in group I, 60.5% patients in groups II and 69.2% patients in groups IIII were 5~15 mg/L. When tested on Matzke method had the lowest area under the ROC curve, AUC 0.501 (0.392-0.611 95% C.I.) for peak level and AUC 0.517 (0.406-0.627 95% C.I.) for trough level, respeatively. The linear regression analysis showed that the ageing was the confounding favor in predicting vancomycin serum concentration. Conclusions Matzke nomogram was shown to achieve target plasma levels (5~15 mg/L) of vancomycin at a higher rate, but lack of convincing evidence of a correlation between serum concentrations and therapeutic outcome. Secondly, little comparative information is currently available as to the dosing of vancomycin in post-adolescent patient populations. This simulation indicated that the Matzke nomogram dosing interval was the most successful method for initial dose selection, but early serum concentration monitoring and adjustment of initial empirical and nomogram-derived doses is necessary.
Nadeshalingam, Gobinath. "Oxygenation-sensitive cardiovascular magnetic resonance imaging (OS-CMR) : potential confounding factors in use of OS-CMR." Thèse, 2015. http://hdl.handle.net/1866/13794.
Background: Oxygenation-sensitive cardiovascular magnetic resonance (OS-CMR) has become a feasible diagnostic imaging modality for monitoring changes of myocardial oxygenation. This technique has great potential for use as a primary diagnostic tool for cardiovascular disease, particularly non-invasive detection of ischemia. Yet, there are several potential confounding factors of this technique, some methodological, such as sequence parameters and others are physiological and not well understood. Due to T2 effects caused by tissue water content, the hydration status may impact signal intensity. This is one physiological aspect in particular that we aimed at quantifying the confounding effect by manipulating hydration status in humans and observing signal intensity (SI) changes in OS-CMR images. Methods: In vitro: Arterial and venous blood from eight swine were used to assess serial dilution of blood and it corresponding effect on OS sequence signal intensity. In vivo: Twenty-two healthy volunteers underwent OS-CMR. Hemoglobin (Hb) concentrations were measured at baseline and immediately following rapid crystalloid infusion of 1,000ml of Lactated Ringer’s solution (LRS). OS-CMR images were acquired in a mid-ventricular short axis view. Myocardial SI was measured during a maximal voluntary breath-hold, after a 60-second period of hyperventilation. SI changes were expressed relative to baseline (% change). Results: The infusion resulted in a significant decrease in measured Hb (142.5±3.3 vs. 128.8±3.3 g/L; p<0.001), while SI increased by 3.2±1.2% between baseline images at normo- and hypervolemia (p<0.05). Both hyperventilation SI and the SI changes induced by apnea were attenuated after hemodilution (p<0.05). Quantitative assessment showed a negative correlation between T2* and hemoglobin concentration (r=-0.46, p<0.005). Conclusions: There are several confounders to the OS-CMR technique that require attention and optimization for future larger scale clinical implementation. The hydration status in particular may be a confounder in OS-CMR imaging. Hypervolemia leads to an increase in SI at baseline and attenuates the SI response during vasoactive breathing maneuvers. This attenuation in signal intensity would need to be accounted for and corrected in clinical assessment of OS-CMR images.
Begum, Mumtaz. "The incidence, risk factors and implications of type 1 diabetes: whole-of-population linked-data study of children in South Australia born from 1999-2013." Thesis, 2020. http://hdl.handle.net/2440/128227.
Thesis (Ph.D.) -- University of Adelaide, School of Public Health, 2020