Tied Survival Times In Survival Analysis

Survival analysis is generally defined as a set of methods for analyzing data where the outcome variable is the time until the occurrence of an event of interest. One of the methods commonly used in the survival analysis is Cox regresion model which is used to determine the factors that impact on survival times. Cox regression model has assumptions. One of them is proportional hazards assumption and the another one is there is no tied data between event times. However, in real applications, tied event times are commonly observed and Cox's partial likelihood function needs to be modified to handle ties. It is well known methods that the Exact method, Breslow method, Efron method and Discrete method for handling tied event times. Firstly, the methods are analysed during the study, Breslow, Efron and Exact methods, which is applied on a stomach canser data set (there is tied data between event times) It was decided that Cox regression with Exact Method is the best model. Than this methods is applied Acute Myocardial Infarction data set which has no tied data between event times and it is found the same resuts at all methods

YAŞAM VERİLERİNİN META-ANALİZİ

Özet: Bir olay zamanı ile ilgilenen ve durdurulmuş veri içeren çalışmaları birleştirmek için özel yöntemlere ihtiyaç vardır. Çalışmada yaşam verilerinden elde edilen sonuçları birleştiren farklı yaklaşımlar incelenmiş ve retroperitoneal sarkomlarla ilgili yapılan makalelerden elde edilen verilere meta-analizi uygulanmıştır. Uygulama sonucunda, tümörün rezeksiyon tipi, tümör grade'i, tümör boyutu, başvuruda tümörün konumu ve cerrahi sınırların konumu değişkenlerinin retroperitoneal sarkomlar için önemli değişkenler olduğu sonucuna varılmıştır. Anahtar kelimeler: Meta-analizi, yaşam analizi, retroperitoneal sarkomlar META-ANALYSIS OF SURVIVAL DATA Abstract: Special methods are needed if one wishes to combine studies whose outcome of interest is time to an event, and data is censored. In this study, several different approaches to combining survival data are investigated. Meta-analysis is applied to data from the papers about retroperitoneal sarcomas. The application results show that the resection type, grade, size and presentation status of the tumor and surgical margin variables are important for retroperitoneal sarcomas. Key words: Meta-analysis, survival analysis, retroperitoneal sarcoma

Bayesian Estimator of a Change Point in the Hazard Function

This article presents a new approach for obtaining the change point in the hazard function. The proposed approach is developed with the Bayesian estimator. Using a simulation study, mean value and mean square error (MSE) of proposed estimator are obtained and compared with the mean and MSE of traditional estimators. It is showed that the proposed estimator is more efficient than the traditional estimators in many cases. Furthermore, a numerical example is discussed to demonstrate the practice of the proposed estimator

Outliers in Survival Analysis

Survival analysis is a collection of statistical methods for analyzing data where the outcome variable is the time until the occurrence of an event of interest. Outliers in survival anaysis calculated differently from classical regression analysis. Outlier detection methods in survival analysis are commonly carried out based on residuals and residual analysis. In survival analysis, there are different types of residuals that are Cox-Snell, Martingale, Schoenfeld, Deviance, Log-odds and Normal deviance residuals. There are methods which are DFBETA, LMAX and Likelihood Displacement values for detecting influential observations. The residuals are analyzed during the study which is applied on a stomach cancer data set and the outliers are detected. After omitting these outliers, model is set up again and results were found better

Modified Estimators For The Change Point In Hazard Function

We propose the consistent estimators for the change point in hazard function by improving the estimators in [A.P. Basu, J.K. Ghosh, S.N. Joshi, On estimating change point in a failure rate, in: S.S. Gupta,J.O. Berger (Eds.), Statistical Decision Theory and Related Topics IV, vol. 2, Springer-Verlag, 1988, pp. 239-252] and [H.T. Nguyen, G.S. Rogers, E.A. Walker, Estimation in change point hazard rate model, Biometrika 71 (1984) 299-304]. By a simulation study, we show that the proposed estimators are more efficient than the original estimators in many cases. (C) 2008 Elsevier B.V. All rights reserved

Yaşam Çözümlemesinde Hızlandırılmış Başarısızlık Süresi Modelleri ve Bir Uygulama

The Cox regression model is the most commonly used regression model for survival data. The Cox regression model has an important assumption that hazard rates are proportional over time. The accelerated failure time model is an alternative method for the analysis of survival data when hazards are not proportional. The accelerated failure time models should lead to more efficient parameter estimates than Cox model under certain circumferences. In this study, The accelerated failure time models are described. The data of stomach cancer patients is used to illustrate these models and the results are discusse

A new Bayes

estimate of the change point in the hazard functio

National Practice In Antibiotic Prophylaxis In Breast Cancer Surgery

Background Although breast cancer surgery is regarded as a “clean” surgery, surgical site infection (SSI) rates are higher than expected. There is no consensus regarding the use of antibiotic prophylaxis in elective breast surgery. The nationwide survey was conducted to determine the trend of antibiotic prophylaxis in breast cancer among Turkish surgeons. Methods The survey was sent to surgeons who are member of Turkish Surgical Association (TSA) via e-mail from TSA web address. A 15 item web-based survey consisted of surgeon demographics and the use of prophylactic antibiotic in patients with risk factors related to SSI. Results The number of completed questionnaires was 245. The most common antibiotic used was first generation of cephalosporins. A majority of respondents indicated that prophylaxis was preferred in patients with high risk of SSI including preoperative chemotherapy or radiotherapy, older age, diabetes mellitus, immunodeficiency, immediate reconstruction (P < 0.05). However, the use of drain did not significantly influence antibiotic prophylaxis (P = 0.091). Conclusions The use of prophylactic antibiotic was strongly dependent on the presence of some risk factors; however, the variation in current practice regarding antibiotic prophylaxis demonstrated a lack of its effect on preventing SSI after breast cancer surgery.PubMe

Vascular Endothelial Growth Factor (Vegf)-C, Vegf-D, Vegfr-3 And D2-40 Expressions In Primary Breast Cancer: Association With Lymph Node Metastasis

Background. Two members of the vascular endothelial growth factor (VEGF) family, VEGF-C and -D, are known as lymphangiogenic growth factors and play an important role in tumor lymphangiogenesis via activation of the VEGF receptor (VEGFR)-3, which is expressed in lymphatic endothelial cells. D2-40 is a specific antibody for lymphatic vessel density (LVD). Objectives. In the present study, we have aimed to evaluate whether intra-and peri-tumoral D2-40-positive lymphatic vessels affect lymph node metastasis and to investigate the relationship between LVD and lymph node metastasis in breast cancer. Material and methods. We have evaluated the relationships between lymph node metastasis and VEGF-C, VEGF-D, VEGFR-3 and D2-40 expressions in breast cancer cells using immunohistochemistry. VEGF-C, VEGF-D and VEGFR-3 expression were found in tumor cells in the majority of the cases (83.75, 97.5 and 95%, respectively). Results. There was a significant positive relationship between VEGF-D expression and lymph node metastasis (p < 0.05) however no significant association was found in VEGF-C and VEGFR-3 expressions. It was found that patients with high-expression of VEGF-D have a high level of both peri-and intra-tumoral LVD compared to those with low expression of VEGF-D (p < 0.05). Conclusions. Our results support that examination of VEGF-D expression in breast cancer cells may be beneficial in the identification of lymph node metastasis.WoSScopu

Does gender affect asthma control in adult asthmatics?

Kurt, Ozlem Kar/0000-0002-4641-2866; Dursun, A. Berna/0000-0002-6337-6326; Karasoy, Duru/0000-0002-2258-4479WOS: 000337624500004PubMed: 24659211Several studies have shown gender differences in prevalence of asthma but there is little information about asthma control. in this study, we aimed to evaluate the effect of gender on asthma control in adult asthmatics. Medical records of 242 patients older than 18 years of age who regularly visited the allergy unit were evaluated. Standardized asthma questionnaires like the asthma control test (ACT) were performed. ACT scores, clinical characteristics, and demographic data such as smoking status, education, duration and severity of asthma, atopic status, family history of asthma, analgesic hypersensitivity, number of emergency visits, and hospitalization in the previous year were compared based on gender. in this study, 77.3% of the patients were female. Mean age, body mass index, and duration of asthma were 39.0 +/- 0.7, 27.3 +/- 0.3, and 6.6 +/- 0.4 years, respectively. of the total, 14.9% of the patients were smokers. Also, 55.8% of them were graduated from middle school, 22.7% from high school, and 14% from university. Atopy rate was 57%. Analgesic hypersensitivity was found in 18.6% of them. There was 30.2% family history of asthma. the asthma severity was mild in 45.5%, moderate in 40.9%, and severe in 13.6% of the patients. One-third of the patients were admitted to emergency room; 1/10th were hospitalized due to asthma in the previous year. ACT scores indicated complete control in 67.8%, partial control in 17.8%, and uncontrolled asthma in 14.5%. Comparing the results of males with females having asthma, there was no statistically significant difference between the two gender according to ACT scores and clinical characteristics. Finally, the results conclude that there was no effect of gender on asthma control assessed with standardized questionnaire in adult asthmatics