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Abstract : Survival Functions in the Presence of Several Events and Competing Risks: Estimation and Interpretation Beyond Kaplan-Meier
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Abstract: Evaluation of a therapeutic strategy is complex when the course of a disease is characterized by the occurrence of different kinds of events. Competing risks arise when the occurrence of specific events prevents the observation of other events. A particular case is semi-competing risks when only fatal events can prevent the observation of the non fatal ones. Kaplan-Meier is the most popular method to estimate overall or event free survival. On the other hand when a subset of events is considered and net survival is of concern, different estimators have been proposed. Kaplan-Meier method can be used only under the independence assumptions otherwise estimators based on multivariate distribution of times are needed. If causes of death are unknown, relative survival can approximate net survival only under specific assumptions on the mortality pattern. Kaplan-Meier method cannot be used to estimate crude cumulative incidence of specific events. The aim of this work is to present the survival functions used in competing risks framework, their non parametric estimators and semi parametric estimators for net survival based on Archimedean Copulas. This would be a help for the reader who is not experienced in competing risks analysis. A simulation study is performed to evaluate performances of net survival estimators. To illustrate survival functions in presence of different causes of death and of different kind of events a numerical example is given, a literature dataset on prostate cancer and a case series of breast cancer patients have been analysed. Keywords: Survival analysis, competing risks, crude cumulative incidence, net survival, relative survival, breast cancer.Download Full Article |
Abstract : Determinants of Immunization Among Children Aged 12-23 Months in Ethiopia: A Proportional Odds Model Approach
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Abstract: Childhood immunization is recognized as one of the most cost-effective public health interventions to prevent morbidity and mortality caused by infectious diseases, particularly in a high-endemic setting. According to the 2011 EDHS report by the Central Statistical Agency (CSA) of Ethiopia, nationally, only 24 percent of children age 12-23 months was fully immunized at the time of the survey. The main objective of this study was to identify and describe the determinants of immunization among children aged 12-23 months in Ethiopia. The source of the data was the Ethiopian Demographic and Health Survey conducted in 2011 (EDHS) 2011. In order to meet our objectives descriptive, and ordinal logistic regression (proportional odds model) statistical techniques were used for data analysis using socio-economic and demographic variables as explanatory variables and immunization status of children aged 12-23 months as the response variable. The results of the analysis predicts that place of delivery, wealth index, possession of radio and region were found to be significant determinants for full immunization among children aged 12-23 months in Ethiopia. Keywords: Immunization, Children aged 12-23 months old, Socioeconomic and Demographic factors, Proportional Odds Model.Download Full Article |
Abstract : A Study of Risk Factors for Breast Cancer in a Primary Oncology Clinic in Benghazi-Libya
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Abstract: Introduction: Libya is a North African country classified under the Eastern Mediterranean Regional Office. In response to the general paucity of literature regarding cancer in Libya, this study aims to analyze various risk factors for breast cancer among patients in Benghazi, Libya. Material and Methods: Using records from a major primary oncology clinic, data was gathered from breast cancer patients. A total of 301 patients were diagnosed with breast cancer in the study period. For the purpose of risk factor determination, this hospital-based case control study consisted of 212 recently diagnosed cases of breast cancer attending the oncology clinic at Al-Jamhouria hospital in Benghazi. Age matched controls (n=219) were randomly enrolled from other medical departments of Al-Jamhouria hospital and the general population visiting the hospital. Chi square was used to assess significance of the risk factors and the corresponding odds ratio (O.R.) and 95% CI were calculated to assess the magnitude of associations.
Results:A total of 1478 cases presented to the gynecological oncology clinic at Al-Jamhouria hospital during the period of 2007-2008. Of these cases, around 20% (n=301) were breast cancer patients. The average age of presentation was 49 years + S.D 13 years, with most of the cases (61%, n=184) being premenopausal. Over 90% (n=273) of breast cancer patients are diagnosed at stage II or later. More than 16% of cases seek medical attention when the malignancy has already reached stage IV. Diabetes, hypertension and family history of other malignancies were found to significantly increase the risk of developing breast cancer.
Discussions: A range of socioeconomic risk factors were also analyzed (i.e. parity, breastfeeding etc…) and some were found to be protective. Libyan breast cancer cases are slightly older compared to the rest of the Arab world, but are younger than their counterparts in the West. The major issue in the Libyan scenario is delayed presentation which significantly worsens the prognosis. Hence, all the recommendations focus on increased awareness, the implementation of a national cancer control plan and a national screening program and training healthcare professions in palliative care. Keywords: Breast cancer, Libya, Arab World, Epidemiological studies, Early Detection of Cancer.Download Full Article |
Abstract : Prediction and Identification of Covariates of Intra-cerebral Hemorrhage
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Abstract: The authors investigate the effects of clinical covariates upon the outcome of Intra-cerebral Hemorrhage (ICH) patients by applying a discriminate model of logistic regression. About 985 patients’s data with ICH have been collected using the International classification of diseases; ninth revision codes are also included. Diagnostic codes (434 for stroke and 431 for ICH) were used to identify patients and confirmed by neuro-imaging of the patients using CT scan and MRI. A univariate analysis of 88 covariates was undertaken and 46 of them reached statistical significance at an acceptable level of p < 0.05. The multivariable analysis exhibited a significant negative relationship between ICH and hypertension. The improvement among ICH patients having hypertension was found to be 0.5 with the p=0.001, ARR=0.5, 95% C.I. 0.3 – 0.8. The development among ICH patients using antihypertensive medicine was 1.3 with p = 0.021, ARR=1.3, 95% C.I. 1.0 – 1.6. Thus present study manifested that ICH has strong relationship with use of antihypertensive medicine. The rate of perfection in the patients physiological conditions using antihypertensive medicine at the time of discharge was 2.9 times acquiring p < 0.001, ARR=2.9, 95% C.I. 2.7 – 3.2 as compared to those who could not use antihypertensive medicine. The change in ARR from 1.3 to 2.9 times depict that the exercise of antihypertensive medicine and ICH outcome are positively associated. The fluctuations in ARR of hypertensive range of systolic blood pressure (SBP) also indicate that the blood pressure range and ICH outcome are negatively correlated. The neurological symptomoatology, indistinct speech and double vision are important factors of proposed models. Moreover, a clear decrease was found in mental status from normal to coma in most suitable model. Surgery is an important part of recovery, and estimated that the improvement among the ICH patients, who were treated under surgical aspects, was 1.4 times with significant p-value in the best models. The complication of pneumonia during treatment of ICH subjects has highly significant showing negative correlation with the given outcome variable. The current model has 89.3% area under the curve with sensitivity (82.6%), specificity (81.3%) and p-value (0.308). This indicates that the constructed model bestows the well performance of the ICH outcome and the model is considered as excellent. Keywords: Intracerebral Hemorrhage, clinical covariates, multivariable analysis, logistic regression, Hosmer-Lemeshow test, discriminate model, sensitivity and specificity.Download Full Article |
Abstract : Evaluating Treatment Effect in Multicenter Trials with Small Centers Using Survival Modeling
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Abstract: Clinical trials of rare diseases commonly enlist several centers to achieve recruitment goals. The aim of this study is to examine the estimation of treatment effects for survival outcomes in multicenter clinical trials with varying numbers of centers and few patients per center for rarer disease outcomes (i.e. rare cancers). We modeled the heterogeneity between centers using Cox frailty models to account for the variability in patients and patient care between centers and examined measures of model fit via smoothed functions of a prognostic factor. Through a simulation study, we were able to examine the consequence of having only a few centers or a few patients per center on the treatment and prognostic factor effects and model performance indices. Overall, we found it is preferable to have more patients per site and more sites in a multicenter trial as expected. However, having a few patients per site is feasible if there are many sites in a trial. Keywords: Frailty, survival, clinical trial, prognostic factor, rare disease.Download Full Article |