920 resultados para Bayesian statistical decision theory


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Einleitung Aktuelle empirische Befunde deuten darauf hin, dass Sportler/innen durch Stress und erhöhte Angst eine reduzierte Effizienz bei der Entscheidungsfindung aufweisen (Wilson, 2008). Erklärt werden kann dieser Befund durch die Attentional-Control-Theory (ACT, Eysenck et al., 2007), die postuliert, dass aufmerksamkeitslenkende Prozesse unter Angst gestört werden. Um diese Annahme für komplexe Situationen im Sport zu prüfen, wurden Fußballspieler unter erhöhten und regulären Druckbedingungen verglichen. Methode Je 11 Experten und Nicht-Experten hatten aus der Perspektive des Abwehrspielers die Aufgabe, in zwei mal 24 Spielsituationen so schnell und korrekt wie möglich verbal anzugeben, welche Aktion der ballführende Spieler (in naher vs. ferner Spielsituation) nach Ausblendung der Szene ausführen wird. Während im ersten Block der Druck nicht erhöht wurde, wurden Druckbedingungen im zweiten Block u.a. durch eine Wettkampfsituation und „falscher“ Ergebnisrückmeldung gesteigert. Entscheidungs- und Blickverhalten (u.a. Anzahl Fixationen), Pupillengröße, Zustandsangst und „Mental Effort“ (Wilson, 2008) wurden erfasst. Neben Expertiseunterschieden wurde erwartet, dass erhöhte Angst die Entscheidungseffizienz sowie das Blickverhalten stört (ACT-Annahme), was mit 2 (Experten/Nicht-Experten) x 2 (nahe/ferne Spielsituation) x 2 (hohe/reguläre Druckbedingung) ANOVAs (? = .05) mit Messwiederholungen auf den letzten beiden Faktoren geprüft wurde. Ergebnisse Druckmanipulationen führten zu höherer Zustandsangst und größeren Pupillendurchmessern. Neben Expertiseunterschieden – Experten antworteten schneller, korrekter und zeigten ein situationsangepasstes visuelles Suchverhalten – wiesen beide Gruppen in Drucksituationen längere Antwortzeiten und höheren Mental Effort auf. Erhöhter Druck führte bei Experten zur Reduktion der Fixationsortwechsel für ferne Spielsituationen. Nicht-Experten differenzierten ihr Suchverhalten weder zwischen Bedingungen noch für Spielsituationen. Diskussion Die Resultate bestätigen die ACT-Annahme, dass Angst und Stress die sportliche Leistung durch längere Reaktionszeiten, höhere kognitive Anstrengung und ein teilweise ineffizientes visuelles Suchverhalten negativ beeinflusst. Eine gestörte Balance zwischen Top-Down und Bottom-Up-Prozessen könnte die Ursache sein (Eysenck et al., 2007). Literatur Eysenck, M. W., Derakshan, N., Santos, R., & Calvo, M. G. (2007). Anxiety and cognitive performance: Attentional control theory. Emotion, 7, 336–353. Wilson, M. (2008). From processing efficiency to attentional control: A mechanistic account of the anxiety-performance relationship. International Review of Sport and Exercise Psychology, 1, 184– 201. 2 Vorträge und Poster

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Although prior research on new venture creation has identified several antecedents that differentiate entrepreneurs from non-entrepreneurs, scholars still have an incomplete understanding of the factors and decision processes that lead an individual to become an entrepreneur. By applying prospect theory, we introduce the reference point as an important antecedent of new venture creation. Testing our research model and hypotheses with entrepreneurs and employees, results show that entrepreneurs set more aspiring reference points and therefore find themselves more often in a perceived loss situation. Results are also robust when testing for entrepreneurial intention of business graduate students. According to prospect theory, the perceived loss triggers more risk-seeking behavior. Summing up, the reference point has a positive effect on new venture creation and differentiates entrepreneurs from nonentrepreneurs. We discuss theoretical and managerial implications of the findings and develop avenues for future research.

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The central assumption in the literature on collaborative networks and policy networks is that political outcomes are affected by a variety of state and nonstate actors. Some of these actors are more powerful than others and can therefore have a considerable effect on decision making. In this article, we seek to provide a structural and institutional explanation for these power differentials in policy networks and support the explanation with empirical evidence. We use a dyadic measure of influence reputation as a proxy for power, and posit that influence reputation over the political outcome is related to vertical integration into the political system by means of formal decision-making authority, and to horizontal integration by means of being well embedded into the policy network. Hence, we argue that actors are perceived as influential because of two complementary factors: (a) their institutional roles and (b) their structural positions in the policy network. Based on temporal and cross-sectional exponential random graph models, we compare five cases about climate, telecommunications, flood prevention, and toxic chemicals politics in Switzerland and Germany. The five networks cover national and local networks at different stages of the policy cycle. The results confirm that institutional and structural drivers seem to have a crucial impact on how an actor is perceived in decision making and implementation and, therefore, their ability to significantly shape outputs and service delivery.

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In this work we propose the adoption of a statistical framework used in the evaluation of forensic evidence as a tool for evaluating and presenting circumstantial "evidence" of a disease outbreak from syndromic surveillance. The basic idea is to exploit the predicted distributions of reported cases to calculate the ratio of the likelihood of observing n cases given an ongoing outbreak over the likelihood of observing n cases given no outbreak. The likelihood ratio defines the Value of Evidence (V). Using Bayes' rule, the prior odds for an ongoing outbreak are multiplied by V to obtain the posterior odds. This approach was applied to time series on the number of horses showing clinical respiratory symptoms or neurological symptoms. The separation between prior beliefs about the probability of an outbreak and the strength of evidence from syndromic surveillance offers a transparent reasoning process suitable for supporting decision makers. The value of evidence can be translated into a verbal statement, as often done in forensics or used for the production of risk maps. Furthermore, a Bayesian approach offers seamless integration of data from syndromic surveillance with results from predictive modeling and with information from other sources such as disease introduction risk assessments.

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Based on common aspects of recent models of career decision-making (CDM) a sixphase model of CDM for secondary students is presented and empirically evaluated. The study tested the hypothesis that students who are in later phases possess more career choice readiness and consider different numbers of career alternatives. 266 Swiss secondary students completed measures tapping phase of CDM, career choice readiness, and number of considered career options. Career choice readiness showed an increase with phase of CDM. Later phases were generally associated with a larger increase in career choice readiness. Number of considered career options showed a curve-linear development with fewer options considered at the beginning and at the end of the process. Male students showed a larger variability in their distribution among the process with more male than female students in the first and last phase of the process. Implications for theory and practice are presented.

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Introduction Recruiting and retaining volunteers who are prepared to make a long-term commitment is a major problem for Swiss sports clubs. With the inclusion of external counselling for the change and systematisation of volunteer management, sports clubs have a possibility to develop and defuse problems in spite of existing barriers and gaps in knowledge. To what extent is external counselling for personnel problems effective? It is often observed that standardised counselling inputs lead to varying consequences for sports clubs. It can be assumed that external impulses are interpreted and transformed differently into the workings of the club. However, this cannot be solely attributed to the situational or structural conditions of the clubs. It is also important to consider the underlying decision-making processes of a club. According to Luhmann’s organisational sociological considerations (2000), organisations (sports clubs) have to be viewed as social systems consisting of (communicated) decisions. This means that organisations are continually reproduced by decision-making processes. All other (observable) factors such as an organisation’s goals, recruiting strategies, support schemes for volunteers etc., have to be seen as an outcome of the operation of prior organisational decisions. Therefore: How do decision-making processes in sports clubs work in the context of the implementation of external counselling? Theoretical Framework An examination of the actual situation in sports clubs shows that decisions frequently appear to be shaped by inconsistency, unexpected outcomes, and randomness (Amis & Slack, 2003). Therefore, it must be emphasised that these decisions cannot be analysed according to any rational decision-making model. Their specific structural characteristics only permit a limited degree of rationality – bounded rationality. Non-profit organisations in particular are shaped by a specific mode of decisionmaking that Cohen, March, and Olsen (1972) have called the “garbage can model”. As sport clubs can also be conceived as “organised anarchies”, this model seems to offer an appropriate approach to understanding their practices and analysing their decision-making processes. The key concept in the garbage can model is the assumption that decision-making processes in organisations consist of four “streams”: (a) problems, (b) actors, (c) decision-making opportunities, and (d) solutions. Method Before presenting the method of the analysis of the decision-making processes in sports clubs, the external counselling will be described. The basis of the counselling is generated by a sports clubs’ capability to change. Due to the specific structural characteristics and organisational principles, change processes in sports clubs often merge with barriers and restrictions. These need to be considered when developing counselling guidelines for a successful planning and realisation of change processes. Furthermore, important aspects of personnel management in sports clubs and especially volunteer management must be implied in order to elaborate key elements for the counselling to recruit new volunteers (e.g., approach, expectations). A counselling of four system-counselling workshops was conceptualised by considering these specific characteristics. The decision-making processes in the sports clubs were analysed during the counselling and the implementation process. A case study is designed with the appropriate methodological approach for such explorative research. The approach adopted for these single case analyses was oriented toward the research program of behavioural decision-making theory (garbage can model). This posits that in-depth insights into organisational decision-making processes can only be gained through relevant case studies of existing organisational situations (Skille, 2013). Before, during and after the intervention, questionnaires and guided interviews were conducted with the project teams of the twelve par-ticipating football clubs to assess the different components of the “streams” in the context of external counselling. These interviews have been analysed using content analysis following guidelines as for-mulated by Mayring (2010). Results The findings show that decision-making processes in football clubs occur differently in the context of external counselling. Different initial positions and problems are the triggers for these decision-making processes. Furthermore, the implementation of the solutions and the external counselling is highly dependent on the commitment of certain people as central players within the decision-mak-ing process. The importance of these relationships is confirmed by previous findings in regard to decision-making and change processes in sports clubs. The decision-making processes in sports clubs can be theoretically analysed using behavioural decision-making theory and the “garbage can model”. Bounded rationality characterises all “streams” of the decision-making processes. Moreo-ver, the decision-making process of the football clubs can be well illustrated in the framework, and the interplay of the different dimensions illustrates the different decision-making practices within the football clubs. References Amis, J., & Slack, T. (2003). Analysing sports organisations: Theory and practice. In B. Houlihan (Eds.), Sport & Society (pp. 201–217). London, England: Sage. Cohen, M.D., March, J.G., & Olsen, J.P. (1972). A garbage can model of organisational choice. Ad-ministrative Science Quarterly, 17, 1-25. Luhmann, N. (2000). Organisation und Entscheidung. Opladen: Westdeutscher Verlag. Mayring, P. (2010). Qualitative Inhaltsanalyse. Grundlagen und Techniken. Weinheim: Beltz. Skille, E. Å. (2013). Case study research in sport management: A reflection upon the theory of science and an empirical example. In S. Söderman & H. Dolles (Eds.), Handbook of research on sport and business (pp. 161–175). Cheltenham, England: Edward Elgar.

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Synchronizing mind maps with fuzzy cognitive maps can help to handle complex problems with many involved stakeholders by taking advantage of human creativity. The proposed approach has the capacity to instantiate cognitive cities by including cognitive computing. A use case in the context of decision-finding (concerning a transportation system) is presented to illustrate the approach.

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I develop the argument that our current decision-making framework, utility theory, when used by itself, is 1) descriptively incomplete, 2) theoretically flawed, and 2) ethically questionable. In response, I offer an exploratory framework that incorporates both consequentialist and non-consequentialist motivations. Adding a commitment function provides a synthesis which remedies the problems associated with the sole use of utility theory. Finally, I show how philosophers Immanuel Kant, W.D. Ross, and Martin Buber provide an ethical basis for the framework.

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BACKGROUND: While significant strides have been made in health research, the incorporation of research evidence into healthcare decision-making has been marginal. The purpose of this paper is to provide an overview of how the utility of health services research can be improved through the use of theory. Integrating theory into health services research can improve research methodology and encourage stronger collaboration with decision-makers. DISCUSSION: Recognizing the importance of theory calls for new expectations in the practice of health services research. These include: the formation of interdisciplinary research teams; broadening the training for those who will practice health services research; and supportive organizational conditions that promote collaboration between researchers and decision makers. Further, funding bodies can provide a significant role in guiding and supporting the use of theory in the practice of health services research. SUMMARY: Institutions and researchers should incorporate the use of theory if health services research is to fulfill its potential for improving the delivery of health care.

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When conducting a randomized comparative clinical trial, ethical, scientific or economic considerations often motivate the use of interim decision rules after successive groups of patients have been treated. These decisions may pertain to the comparative efficacy or safety of the treatments under study, cost considerations, the desire to accelerate the drug evaluation process, or the likelihood of therapeutic benefit for future patients. At the time of each interim decision, an important question is whether patient enrollment should continue or be terminated; either due to a high probability that one treatment is superior to the other, or a low probability that the experimental treatment will ultimately prove to be superior. The use of frequentist group sequential decision rules has become routine in the conduct of phase III clinical trials. In this dissertation, we will present a new Bayesian decision-theoretic approach to the problem of designing a randomized group sequential clinical trial, focusing on two-arm trials with time-to-failure outcomes. Forward simulation is used to obtain optimal decision boundaries for each of a set of possible models. At each interim analysis, we use Bayesian model selection to adaptively choose the model having the largest posterior probability of being correct, and we then make the interim decision based on the boundaries that are optimal under the chosen model. We provide a simulation study to compare this method, which we call Bayesian Doubly Optimal Group Sequential (BDOGS), to corresponding frequentist designs using either O'Brien-Fleming (OF) or Pocock boundaries, as obtained from EaSt 2000. Our simulation results show that, over a wide variety of different cases, BDOGS either performs at least as well as both OF and Pocock, or on average provides a much smaller trial. ^

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The joint modeling of longitudinal and survival data is a new approach to many applications such as HIV, cancer vaccine trials and quality of life studies. There are recent developments of the methodologies with respect to each of the components of the joint model as well as statistical processes that link them together. Among these, second order polynomial random effect models and linear mixed effects models are the most commonly used for the longitudinal trajectory function. In this study, we first relax the parametric constraints for polynomial random effect models by using Dirichlet process priors, then three longitudinal markers rather than only one marker are considered in one joint model. Second, we use a linear mixed effect model for the longitudinal process in a joint model analyzing the three markers. In this research these methods were applied to the Primary Biliary Cirrhosis sequential data, which were collected from a clinical trial of primary biliary cirrhosis (PBC) of the liver. This trial was conducted between 1974 and 1984 at the Mayo Clinic. The effects of three longitudinal markers (1) Total Serum Bilirubin, (2) Serum Albumin and (3) Serum Glutamic-Oxaloacetic transaminase (SGOT) on patients' survival were investigated. Proportion of treatment effect will also be studied using the proposed joint modeling approaches. ^ Based on the results, we conclude that the proposed modeling approaches yield better fit to the data and give less biased parameter estimates for these trajectory functions than previous methods. Model fit is also improved after considering three longitudinal markers instead of one marker only. The results from analysis of proportion of treatment effects from these joint models indicate same conclusion as that from the final model of Fleming and Harrington (1991), which is Bilirubin and Albumin together has stronger impact in predicting patients' survival and as a surrogate endpoints for treatment. ^

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Standard methods for testing safety data are needed to ensure the safe conduct of clinical trials. In particular, objective rules for reliably identifying unsafe treatments need to be put into place to help protect patients from unnecessary harm. DMCs are uniquely qualified to evaluate accumulating unblinded data and make recommendations about the continuing safe conduct of a trial. However, it is the trial leadership who must make the tough ethical decision about stopping a trial, and they could benefit from objective statistical rules that help them judge the strength of evidence contained in the blinded data. We design early stopping rules for harm that act as continuous safety screens for randomized controlled clinical trials with blinded treatment information, which could be used by anyone, including trial investigators (and trial leadership). A Bayesian framework, with emphasis on the likelihood function, is used to allow for continuous monitoring without adjusting for multiple comparisons. Close collaboration between the statistician and the clinical investigators will be needed in order to design safety screens with good operating characteristics. Though the math underlying this procedure may be computationally intensive, implementation of the statistical rules will be easy and the continuous screening provided will give suitably early warning when real problems were to emerge. Trial investigators and trial leadership need these safety screens to help them to effectively monitor the ongoing safe conduct of clinical trials with blinded data.^

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Bayesian adaptive randomization (BAR) is an attractive approach to allocate more patients to the putatively superior arm based on the interim data while maintains good statistical properties attributed to randomization. Under this approach, patients are adaptively assigned to a treatment group based on the probability that the treatment is better. The basic randomization scheme can be modified by introducing a tuning parameter, replacing the posterior estimated response probability, setting a boundary to randomization probabilities. Under randomization settings comprised of the above modifications, operating characteristics, including type I error, power, sample size, imbalance of sample size, interim success rate, and overall success rate, were evaluated through simulation. All randomization settings have low and comparable type I errors. Increasing tuning parameter decreases power, but increases imbalance of sample size and interim success rate. Compared with settings using the posterior probability, settings using the estimated response rates have higher power and overall success rate, but less imbalance of sample size and lower interim success rate. Bounded settings have higher power but less imbalance of sample size than unbounded settings. All settings have better performance in the Bayesian design than in the frequentist design. This simulation study provided practical guidance on the choice of how to implement the adaptive design. ^

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In recent years, disaster preparedness through assessment of medical and special needs persons (MSNP) has taken a center place in public eye in effect of frequent natural disasters such as hurricanes, storm surge or tsunami due to climate change and increased human activity on our planet. Statistical methods complex survey design and analysis have equally gained significance as a consequence. However, there exist many challenges still, to infer such assessments over the target population for policy level advocacy and implementation. ^ Objective. This study discusses the use of some of the statistical methods for disaster preparedness and medical needs assessment to facilitate local and state governments for its policy level decision making and logistic support to avoid any loss of life and property in future calamities. ^ Methods. In order to obtain precise and unbiased estimates for Medical Special Needs Persons (MSNP) and disaster preparedness for evacuation in Rio Grande Valley (RGV) of Texas, a stratified and cluster-randomized multi-stage sampling design was implemented. US School of Public Health, Brownsville surveyed 3088 households in three counties namely Cameron, Hidalgo, and Willacy. Multiple statistical methods were implemented and estimates were obtained taking into count probability of selection and clustering effects. Statistical methods for data analysis discussed were Multivariate Linear Regression (MLR), Survey Linear Regression (Svy-Reg), Generalized Estimation Equation (GEE) and Multilevel Mixed Models (MLM) all with and without sampling weights. ^ Results. Estimated population for RGV was 1,146,796. There were 51.5% female, 90% Hispanic, 73% married, 56% unemployed and 37% with their personal transport. 40% people attained education up to elementary school, another 42% reaching high school and only 18% went to college. Median household income is less than $15,000/year. MSNP estimated to be 44,196 (3.98%) [95% CI: 39,029; 51,123]. All statistical models are in concordance with MSNP estimates ranging from 44,000 to 48,000. MSNP estimates for statistical methods are: MLR (47,707; 95% CI: 42,462; 52,999), MLR with weights (45,882; 95% CI: 39,792; 51,972), Bootstrap Regression (47,730; 95% CI: 41,629; 53,785), GEE (47,649; 95% CI: 41,629; 53,670), GEE with weights (45,076; 95% CI: 39,029; 51,123), Svy-Reg (44,196; 95% CI: 40,004; 48,390) and MLM (46,513; 95% CI: 39,869; 53,157). ^ Conclusion. RGV is a flood zone, most susceptible to hurricanes and other natural disasters. People in the region are mostly Hispanic, under-educated with least income levels in the U.S. In case of any disaster people in large are incapacitated with only 37% have their personal transport to take care of MSNP. Local and state government’s intervention in terms of planning, preparation and support for evacuation is necessary in any such disaster to avoid loss of precious human life. ^ Key words: Complex Surveys, statistical methods, multilevel models, cluster randomized, sampling weights, raking, survey regression, generalized estimation equations (GEE), random effects, Intracluster correlation coefficient (ICC).^

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Many public health agencies and researchers are interested in comparing hospital outcomes, for example, morbidity, mortality, and hospitalization across areas and hospitals. However, since there is variation of rates in clinical trials among hospitals because of several biases, we are interested in controlling for the bias and assessing real differences in clinical practices. In this study, we compared the variations between hospitals in rates of severe Intraventricular Haemorrhage (IVH) infant using Frequentist statistical approach vs. Bayesian hierarchical model through simulation study. The template data set for simulation study was included the number of severe IVH infants of 24 intensive care units in Australian and New Zealand Neonatal Network from 1995 to 1997 in severe IVH rate in preterm babies. We evaluated the rates of severe IVH for 24 hospitals with two hierarchical models in Bayesian approach comparing their performances with the shrunken rates in Frequentist method. Gamma-Poisson (BGP) and Beta-Binomial (BBB) were introduced into Bayesian model and the shrunken estimator of Gamma-Poisson (FGP) hierarchical model using maximum likelihood method were calculated as Frequentist approach. To simulate data, the total number of infants in each hospital was kept and we analyzed the simulated data for both Bayesian and Frequentist models with two true parameters for severe IVH rate. One was the observed rate and the other was the expected severe IVH rate by adjusting for five predictors variables for the template data. The bias in the rate of severe IVH infant estimated by both models showed that Bayesian models gave less variable estimates than Frequentist model. We also discussed and compared the results from three models to examine the variation in rate of severe IVH by 20th centile rates and avoidable number of severe IVH cases. ^