Osman DagHacettepe University · Department of Biostatistics
Osman Dag
Associate Professor of Biostatistics
About
47
Publications
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Introduction
Dr. Osman Dag currently works at the Department of Biostatistics, Hacettepe University. Osman does research in Biostatistics. His most recent publication is 'Diverse Classifiers Ensembe Based on GMDH Algorithm for Binary Classification'.
Publications
Publications (47)
Multiple comparison methods are applied to control the type I error rate at the nominal level. In this study, we investigate the performance of multiple comparison methods after analysis of variance (ANOVA) is implemented under different conditions. We include Bonferroni, Holm, Hochberg, Hommel, Benjamini-Hochberg (BH), and Benjamini-Yekutieli (BY)...
Background/aims:
Inborn errors of immunity (IEI) may associate with autoimmune diseases, including autoimmune liver diseases (AILD). However, both the IEI frequency and secondary effects of immunosuppressives are unknown in patients with AILD due to the lack of data. We aimed to evaluate the ratio of IEI in AILD.
Materials and methods:
A total o...
Purpose: To compare dry eye findings in diabetes mellitus patients with and without diabetic foot. Methods: Diabetes mellitus patients with and without diabetic foot were included in this controlled cross-sectional study. Tear break-up time (BUT) and Schirmer test results of each participant were noted. Ocular Surface Disease Index (OSDI) questionn...
Amaç: Dikkat Eksikliği Hiperaktivite Bozukluğu (DEHB) yaşa ve gelişim düzeyine uygun olmayan dikkatsizlik, hiperaktivite ve dürtüsellik ile karakterize nörogelişimsel bir bozukluktur. Okul çağı çocuklarda kliniklere başvuru sıklığı oldukça artmaktadır. Bu araştırma okul çağı DEHB’li çocuklarda kombine egzersiz eğitiminin fiziksel uygunluk, yürüme h...
Background&aims:
Cystic fibrosis (CF) -related bone disease (CFBD) is an important complication of CF, and low BMD in childhood is a precursor of CFBD. Here, we aimed to investigate bone turnover biomarkers, including osteocalcin (OC), receptor activator of nuclear factor kappa B ligand (RANKL) and osteoprotegerin (OPG) in relation to low BMD in c...
This article presents two approaches to extend classical MANOVA tests to the unequal covariances case. The first approach is illustrated by extending the classical Wilks test, which is valid only when covariances are equal. Such tests will be based on exact probabilities of certain extreme regions. We will also show how tests numerically equivalent...
This study was carried out to examine the relationship between physical activity (PA) levels of secondary school students and their safe environment, playing conditions and media usage. The sample of the study was consisted of 628 students aged between 11-14 years old. The universe of the study was composed of students studying in the secondary sch...
Objective:
The aim of the current study was to compare the spatio-temporal parameters of gait and gross motor skills in children with attention deficit hyperactivity disorder-combined type with those of typically developing children and to search the effect of motor skills on gait parameters in children with attention deficit hyperactivity disorde...
This study aimed to determine the effects of a 6-week stroboscopic balance training program on balance scores in athletes with chronic ankle instability. Balance was evaluated before and after the 6-week balance training program. After the program, there were no differences between the strobe and nonstrobe groups in static balance. In terms of dyna...
Background:
Drug addiction is one of the alarming public health and social problems in Afghanistan and around the world. Addiction denotes the habitual use or the physical or mental dependence on narcotic drugs or psychotropic substances.
Methods:
Drug addicts who were admitted to six public addicts' rehabilitation centers in Herat, Afghanistan...
This study aims to develop a valid and reliable scale to assess whether a physician is inclined to take conscientious objection when asked to perform medical services that clash with his/her personal beliefs. The scale, named the Inclination toward Conscientious Objection Scale, was developed for physicians in Turkey. Face validity, content validit...
Chronic ankle instability (CAI) is characterized by repetitive episodes or perceptions of the ankle giving way; ongoing symptoms such as pain, weakness, or reduced ankle range of motion (ROM); diminished self-reported function; and recurrent ankle sprains for more than a year after the initial injury. 1 Gait modifications may result from mechanical...
Selection of differentially expressed genes (DEGs) is a vital process to discover the causes of diseases. It has been shown that modelling of genomics data by considering relation among genes increases the predictive performance of methods compared to univariate analysis. However, there exist serious differences among most studies analyzing the sam...
Background
We aimed to investigate the immuno-histochemical expression of C4d, ADAM10 and WT1 in kidney biopsies of immunoglobulin A nephropathy (IgAN) patients and correlate the findings with clinical, laboratory and histopathologic features in the hope of defining new parameters to better understand the pathogenesis of the disease, and predict pr...
Background:
Seroepidemiology, risk factors to hepatitis E virus exposure, and prevalence of hepatitis E virus viremia have not yet been investigated among patients under immunosuppression or with liver disease that are high risk for infection in Turkey.
Methods:
In this cross-sectional study, 292 consecutive serum samples from renal transplant r...
In this article we derive two simple tests for two-way ANOVA under unequal variances requiring some constraints, which cannot be solved by classical regression formulas. We do so by taking the generalized p-value approach and provide explicit formulas to handle the constraints. The first test is an extension of fiducial one-way ANOVA test, which te...
Normal distribution has a vital role for the most of statistical methods. Box-Cox power transformation is the most usually applied method when the distribution of data is not normal. In this study, a novel algorithm is proposed assembling different Box-Cox transformation estimates of the well performed six techniques proposed by Asar et al. (2017)...
We aimed to characterize the epidemiology and clinical outcomes of patients with bloodstream infections (BSIs) due to carbapenem-resistant Klebsiella pneumoniae (CRKP) in an OXA-48 predominant environment. This was a retrospective single-center cohort study including all consecutive patients with CRKP BSIs treated between 01.01.2014 and 31.12.2018....
Although chronic multi-site musculoskeletal pain is known to cause decreased physical function and impair work and social life, there is insufficient research about its impact on health-related quality of life (HRQoL) in women. The aim of this study was to investigate multiple factors affecting HRQoL in women with chronic multi-site musculoskeletal...
We compared the rates of acute kidney injury (AKI), 7-day and 30-day mortalities, and resolution of AKI at discharge in combination therapies involving either teicoplanin (TEI) or vancomycin (VAN) with piperacillin-tazobactam (TZP) or meropenem (MER). In a single-center, retrospective cohort study, adult patients (>18 years) who had a baseline seru...
Objectives
To investigate the effect of a 6-week stroboscopic balance training program on cortical activities in athletes with chronic ankle instability.
Design
Randomized controlled trial. Setting: Single-center.
Participants
Thirty-nine participants were assigned to the strobe group (SG, n = 13), non-strobe group (NSG, n = 13), and control grou...
Purpose:
Physical inactivity is an important determinant of chronic disease such as obesity, cardiovascular disease and certain types of cancer. Therefore, evaluation of physical activity becomes more important day by day. The purpose of the present study was to investigate the validity, reliability and Turkish version of The Recent Physical Activ...
Background
The renal transplant recipients (RT), allogeneic hematopoietic stem cell transplant recipients (allo-HSCT), patients with acute hepatitis (AH), and chronic hepatitis C patients (CHC) are at risk of hepatitis E virus (HEV) infection. However, seroepidemiology, risk factors to HEV exposure, and the prevalence of HEV viremia has not yet bee...
Background/aim:
Hepatitis B virus (HBV) vaccination rates are insufficient in high-risk patients worldwide. This study aimed to investigate the screening, immunization, and vaccination rates in three high-risk groups for HBV infection: allogeneic hematopoietic stem cell transplantation (AHSCT), renal transplantation (RT), and chronic hepatitis C (...
Background/aims:
Chronic hepatitis C (CHC) is the only viral infection that can be treated with oral antiviral agents. However, CHC awareness is a major barrier to the World Health Organization's target of eliminating hepatitis C virus (HCV) by 2030. Here, CHC awareness trends were analyzed in Hacettepe University Hospital, Turkey, between January...
Improvement of the harmony between facial subunits is the ultimate goal of orthognathic surgery and surgeons must accurately make soft tissue projections for planned bony movements. Yet, few studies have examined the effects’ of orthognathic surgery on aesthetic parameters of nasolabial area on a thorough basis.
This retrospective study included 61...
Group Method of Data Handling (GMDH) - type neural network algorithm is the heuristic self-organizing algorithm to model the sophisticated systems. In this study, we propose a new algorithm assembling different classifiers based on GMDH algorithm for binary classification. A Monte Carlo simulation study is conducted to compare diverse classifier en...
Background
Colistin is a last resort antibiotic against infections with CRKp. Its increased use has led to resistance to this antibiotic.
Methods
This was a single-center, retrospective, cohort study including all CRKp BSIs treated between January 1, 2014 and July 31, 2018. Antibiotic therapy was appropriate if initiated within 5 days from the ons...
Group method of data handling (GMDH)-type neural network algorithms are the self-organizing algorithms for modeling complex systems. GMDH algorithms are used for different objectives; examples include regression, classification, clustering, forecasting, and so on. In this paper, we present GMDH2 package to perform binary classification via GMDH-typ...
Introduction:
Modern rhinoplasty has an aesthetic and a functional component that cannot be separated. Functional rhinoplasty generally concentrates on optimizing nasal airflow. Numerous techniques have been described for correction of each pathology. There seems to be a consensus on the benefit of surgery to patients with nasal obstruction. Prese...
Aim: Red blood cell transfusion may be inevitable in cardiac surgery due to both blood loss and hemodilution secondary to cardiopulmonary bypass. Transfusion strategies may change over time owing to technological advances. The aim of this study was to evaluate the effect of the patient blood management education applied to healthcare staff on the n...
Aim: Cardiac arrest during cardiopulmonary bypass (CPBP) is achieved using cardioplegia solutions for myocardial protection. There are limited data about the systemic biochemical effects of cardioplegia solutions. This study aimed to compare the biochemical effects of del Nido cardioplegia, blood cardioplegia, and St. Thomas cardioplegia solutions....
Background
VAN has been shown to cause increased incidence of AKI when combined with TZP. The reason is unknown. TEI is a glycopeptide which may be less nephrotoxic. We compared both glycopeptides in combination with TZP or MER for causing AKI.
Methods
A retrospective cohort study was performed between May 2015 and December 2017 in a large tertiar...
One-way tests in independent groups designs are the most commonly utilized statistical methods with applications on the experiments in medical sciences, pharmaceutical research, agri culture, biology, engineering, social sciences and so on. In this paper, we present the onewaytests package to investigate treatment effects on the dependent variable....
Background
Muscle thickness and cross-sectional area (CSA) of the thenar muscles can vary depending on different pathologies (such as neuropathies, arthritis etc.). It is important to evaluate these muscles throughout the diagnosis and treatment processes to understand the pathophysiology of diseases and to identify new treatment strategies. Ultras...
In this study, we construct a feasible region, in which we maximize the likelihood function, by using Shapiro-Wilk and Bartlett's test statistics to obtain Box-Cox power transformation parameter for solving the issues of non-normality and/or heterogeneity of variances in ANOVA. Simulation studies illustrate that the proposed approach is more succes...
Box-Cox power transformation is a commonly used methodology to transform the
distribution of a non-normal data into a normal one. Estimation of the
transformation parameter is crucial in this methodology. In this study, the
estimation process is hold via a searching algorithm and is integrated into
well-known seven goodness of fit tests for normal...
Background and Aim: Interscalene brachial plexus block is a common technique used for perioperative pain management in patients undergoing shoulder surgery. This study aimed to determine the analgesic efficacy and hemodynamic effects of the addition of fentanyl to levobupivacaine interscalene brachial plexus block for shoulder surgery. Material and...
Group Method of Data Handling (GMDH)-type neural network algorithms are the heuristic self organization method for the modelling of complex systems. GMDH algorithms are utilized for a variety of purposes, examples include identification of physical laws, the extrapolation of physical fields, pattern recognition, clustering, the approximation of mul...
Objective:
Chronic obstructive pulmonary disease (COPD), asthma and asthma-COPD overlap syndrome (ACOS) are obstructive pulmonary disorders with different manifestations. Status of oxidation in tissues is important in obstructive pulmonary disorders. Smoking, acute exacerbations of COPD and asthma were associated with a marked imbalance in oxidant...
Researchers mainly investigate the treatment effect on a dependent variable. While comparing more than two groups of treatment effect, normality and homogeneity of variances have important roles affecting the performance of tests. In this study, one-way ANOVA, Welch’s ANOVA, Kruskal Wallis test, Alexander-Govern test, James-Second order test, Brown...
Box-Cox transformation is one of the most commonly used methodologies when data do not follow normal distribution. However, its use is restricted since it usually requires the availability of covariates. In this article, the use of a non-informative auxiliary variable is proposed for the implementation of Box-Cox transformation. Simulation studies...