Papers by Haydar Demirhan
Hacettepe Journal of …, 2006
In this paper, the specification of hyper-parameters of the prior distri-bution of log-linear par... more In this paper, the specification of hyper-parameters of the prior distri-bution of log-linear parameters is taken into account. Determination of a prior for the log-linear parameters is considered. Some approaches are given to specify the covariance matrix of the prior ...
Additional file 1 Supplementary Material for The impact of grey zones on the accuracy of agreemen... more Additional file 1 Supplementary Material for The impact of grey zones on the accuracy of agreement measures for ordinal tables.
Supplemental material, sj-tex-2-smm-10.1177_09622802211037068 for Bayesian approaches to the weig... more Supplemental material, sj-tex-2-smm-10.1177_09622802211037068 for Bayesian approaches to the weighted kappa-like inter-rater agreement measures by Quoc Duyet Tran, Haydar Demirhan and Anil Dolgun in Statistical Methods in Medical Research
Supplemental material, sj-pdf-1-smm-10.1177_09622802211037068 for Bayesian approaches to the weig... more Supplemental material, sj-pdf-1-smm-10.1177_09622802211037068 for Bayesian approaches to the weighted kappa-like inter-rater agreement measures by Quoc Duyet Tran, Haydar Demirhan and Anil Dolgun in Statistical Methods in Medical Research
Statistica Neerlandica, 2008
In this paper, Bayesian estimation of log odds ratios over R × C and 2 × 2 × K contingency tables... more In this paper, Bayesian estimation of log odds ratios over R × C and 2 × 2 × K contingency tables is considered, which is practically reasonable in the presence of prior information. Likelihood functions for log odds ratios are derived for each table structure. A prior specification strategy is proposed. Posterior inferences are drawn using Gibbs sampling and Metropolis-Hastings algorithm. Two numerical examples are given to illustrate the matters argued.
Journal of Statistical Computation and Simulation, 2012
Abstract This article deals with the construction of an X̄ control chart using the Bayesian persp... more Abstract This article deals with the construction of an X̄ control chart using the Bayesian perspective. We obtain new control limits for the X̄ chart for exponentially distributed data-generating processes through the sequential use of Bayes' theorem and credible intervals. Construction of the control chart is illustrated using a simulated data example. The performance of the proposed, standard, tolerance interval, exponential cumulative sum (CUSUM) and exponential exponentially weighted moving average (EWMA) control limits ...
Hacettepe Journal of …, 2006
In this paper, the specification of hyper-parameters of the prior distri-bution of log-linear par... more In this paper, the specification of hyper-parameters of the prior distri-bution of log-linear parameters is taken into account. Determination of a prior for the log-linear parameters is considered. Some approaches are given to specify the covariance matrix of the prior ...
Expert Systems with Applications
BMC Medical Research Methodology
Background In inter-rater agreement studies, the assessment behaviour of raters can be influenced... more Background In inter-rater agreement studies, the assessment behaviour of raters can be influenced by their experience, training levels, the degree of willingness to take risks, and the availability of clear guidelines for the assessment. When the assessment behaviour of raters differentiates for some levels of an ordinal classification, a grey zone occurs between the corresponding adjacent cells to these levels around the main diagonal of the table. A grey zone introduces a negative bias to the estimate of the agreement level between the raters. In that sense, it is crucial to detect the existence of a grey zone in an agreement table. Methods In this study, a framework composed of a metric and the corresponding threshold is developed to identify grey zones in an agreement table. The symmetry model and Cohen’s kappa are used to define the metric, and the threshold is based on a nonlinear regression model. A numerical study is conducted to assess the accuracy of the developed framewor...
International Journal for Equity in Health
BackgroundMeasuring health inequality is essential to ensure that everyone has equal accessibilit... more BackgroundMeasuring health inequality is essential to ensure that everyone has equal accessibility to health care. Studies in the past have continuously presented and showed areas or groups of people affected by various inequality in accessing the health resources and services to help improve this matter. Alongside, disease prevention is as important to minimise the disease burden and improve health and quality of life. These aspects are interlinked and greatly contributes to one’s health.MethodIn this study, the Gini coefficient and Lorenz curve are used to give an indication of the overall health inequality. The impact of this inequality in granular level is demonstrated using Bayesian estimation for disease detection. The Bayesian estimation used a two-component modelling approach that separates the case detection process and incidence rate using a mixed Poisson distribution while capturing underlying spatio-temporal characteristics. Bayesian model averaging is used in conjunctio...
Energy Conversion and Management
IEEE Access, 2022
The Flaming Datum (FD) problem refers to the search for a hostile Evader that is fleeing after mo... more The Flaming Datum (FD) problem refers to the search for a hostile Evader that is fleeing after momentarily revealing its position. If Evader's direction is fixed but unknown, while its maximal speed is known, Koopman argued in 1980 that the best trajectory for Searcher is a spiral starting from the revealed position. The objective of our study is to verify the hypothesis of a spiral search path, by formulating the FD problem in the framework of a finite two-player zero-sum partially observed stochastic search game, where the opponent plays repeatedly a fixed but unknown pure strategy. Using a realistic sensor model, current information about the position of Evader is represented by an occupancy map, updated in the Bayesian framework. The utility is computed as the entropy reduction of the occupancy map. The game was implemented in software and solved using the maxmin method. By running repeatedly the described search game, we have found that the search pattern, although random (due to the uncertainties in sensing and mixed strategies), is indeed a spiral on every play of the game, thus confirming the hypothesis.
Health Care Management Science, 2022
Increasingly, many hospitals are attempting to provide more accurate information about Emergency ... more Increasingly, many hospitals are attempting to provide more accurate information about Emergency Department (ED) wait time to their patients. Estimation of ED wait time usually depends on what is known about the patient and also the status of the ED at the time of presentation. We provide a model for estimating ED wait time for prospective low acuity patients accessing information online prior to arrival. Little is known about the prospective patient and their condition. We develop a Bayesian quantile regression approach to provide an estimated wait time range for prospective patients. Our proposed approach incorporates a priori information in government statistics and elicited expert opinion. This methodology is compared to frequentist quantile regression and Bayesian quantile regression with non-informative priors. The test set includes 1, 024 low acuity presentations, of which 457 (44%) are Category 3, 425 (41%) are Category 4 and 160 (15%) are Category 5. On the Huber loss metric, the proposed method performs best on the test data for both median and 90th percentile prediction compared to non-informative Bayesian quantile regression and frequentist quantile regression. We obtain a benefit in the estimation of model coefficients due to the value contributed by a priori information in the form of elicited expert guesses guided by government wait time statistics. The use of such informative priors offers a beneficial approach to ED wait time prediction with demonstrable potential to improve wait time quantile estimates.
BMC Medical Research Methodology, 2021
Background In an inter-rater agreement study, if two raters tend to rate considering different as... more Background In an inter-rater agreement study, if two raters tend to rate considering different aspects of the subject of interest or have different experience levels, a grey zone occurs among the levels of a square contingency table showing the inter-rater agreement. These grey zones distort the degree of agreement between raters and negatively impact the decisions based on the inter-rater agreement tables. In this sense, it is important to know how the existence of a grey zone impacts the inter-rater agreement coefficients to choose the most reliable agreement coefficient against the grey zones to reach out with more reliable decisions. Methods In this article, we propose two approaches to create grey zones in simulations setting and conduct an extensive Monte Carlo simulation study to figure out the impact of having grey zones on the weighted inter-rater agreement measures for ordinal tables over a comprehensive simulation space. Results The weighted inter-rater agreement coeffici...
Applied Soft Computing, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
European Journal of Science and Mathematics Education, 2014
The different opinions on products and applications of gene technology (GT) draw attention to the... more The different opinions on products and applications of gene technology (GT) draw attention to the training and education activities related to GT. The purpose of this study is to review some variables predicting the acceptance perception regarding GT, and to investigate their changes at levels. The prospective teachers' subjective knowledge and interest levels in relation to the use of GT and their risk and acceptance perceptions have been questioned through a Likert type questionnaire. Latent class and binary logistic regression analyses were used. This study was carried out with 135 prospective biology teachers. According to our study, it is possible to state that there are variables, at 5% level of significance, predicting acceptance of interest and risk variables in terms of GT. As perception towards GT being risky decreases and interest towards GT increases, the acceptance perception regarding GT increases.
Communications in Statistics - Simulation and Computation, 2018
Estimation of the degree of agreement between different raters is of crucial importance in medica... more Estimation of the degree of agreement between different raters is of crucial importance in medical and social sciences. There are lots of different approaches proposed in the literature for this aim. In this article, we focus on the inter-rater agreement measures for the ordinal variables. The ordinal nature of the variable makes this estimation task more complicated. Although there are modified versions of inter-rater agreement measures for ordinal tables, there is no clear agreement on the use of a particular approach. We conduct an extensive Monte Carlo simulation study to evaluate and compare the accuracy of mainstream inter-rater agreement measures for ordinal tables with each other and figure out the effect of different table structures on the accuracy of these measures. Our results are useful in the sense that they provide detailed information about which measure to use with different table structures to get most reliable inferences about the degree of agreement between two raters. With our simulation study, we recommend use of Gwet's AC2 and Brennan-Prediger's j in the situation where there is high agreement among raters. However, it should be noted that these coefficients overstate the extent of agreement among raters when there is no agreement, and the data is unbalanced.
Methods in Ecology and Evolution, 2020
Species sighting records are combined with statistical models to infer whether an endangered spec... more Species sighting records are combined with statistical models to infer whether an endangered species might have become extinct, or instead has just gone unobserved for a lengthy period of time. The challenging part of developing these models lies in dealing with uncertain sightings. We propose a Bayesian hierarchical approach to infer the extinction time of a species based on historical sighting records which may be either certain or uncertain. The posterior distribution for extinction time is evaluated using the likelihood of sighting data and non‐informative priors for model parameters. All the models discussed in this paper are implemented in JAGS, a program for analysing Bayesian models using Markov Chain Monte Carlo (MCMC) simulation. A general methodology is presented and then applied to the sighting record of the ivory‐billed woodpecker (IBW) Campephilus principalis. It was found that the IBW most likely went extinct between 1940 and 1945, a little after the date of the last ...
International Journal of Medical Informatics, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Papers by Haydar Demirhan