Absolute Penalty and Shrinkage Estimation Strategies in Linear and Partially Linear Models

In this dissertation we studied asymptotic properties of shrinkage estimators, and compared their performance with absolute penalty estimators (APE) in linear and partially linear models (PLM). A robust shrinkage M-estimator is proposed for PLM, and asymptotic properties are investigated, both analytically and through simulation studies. In Chapter 2, we compared the performance of shrinkage and some APEs through prediction error criterion in a multiple linear regression setup. In particular, we compared shrinkage estimators with lasso, adaptive lasso and SCAD estimators. Monte Carlo studies were conducted to compare the estimators in two situations: when p \u3c\u3c n, and when p is large yet p \u3c n. Examples using some real data sets are presented to illustrate the usefulness of the suggested methods. In Chapter 3, we developed shrinkage estimators for a PLM. Efficient procedures for simultaneous sub-model selection and shrinkage estimation have been developed and implemented to obtain the parameter estimates where the nonparametric component is estimated using B-spline basis expansion. The proposed shrinkage estimator performed similarly to adaptive lasso estimators. In overall comparison, shrinkage estimators based on B-splines outperformed the lasso for moderate sample sizes and when the nuisance parameter space is large. In Chapter 4, we proposed robust shrinkage M-estimators in a PLM with scaled residuals. Ahmed et al. (2006) considered such an M-estimator in a linear regression setup. We extended their work to a PLM

Statistical properties and different methods of estimation of transmuted Rayleigh distribution

This article addresses the various properties and different methods of estimation of the unknown parameters of the Transmuted Rayleigh (TR) distribution from the frequentist point of view. Although, our main focus is on estimation from frequentist point of view,  yet, various mathematical and statistical properties of the TR distribution (such as quantiles, moments, moment generating function, conditional moments,  hazard rate, mean residual lifetime, mean past lifetime,  mean deviation about mean and median, the stochastic ordering,  various entropies, stress-strength parameter  and order statistics) are derived.  We briefly describe different frequentist methods of estimation approaches, namely, maximum likelihood estimators, moments estimators, L-moment estimators, percentile based estimators, least squares estimators, method of maximum product of spacings,  method of Cram\'er-von-Mises, methods of Anderson-Darling and right-tail Anderson-Darling and compare them using extensive numerical simulations. Monte Carlo simulations are performed to compare the performances of the proposed methods of estimation for both small and large samples. Finally, the potentiality of the model is analyzed by means of two real data sets which is further illustrated by obtaining bias and standard error of the estimates and the bootstrap percentile confidence intervals using bootstrap resampling.Este artículo se aborda las varias propiedades y diferentes métodos para la estimación de los desconocidos parámetros de Transmuted Rayleigh (TR) distribución desde el punto de vista de un frequentist. Aunque la tema principal de este artículo es estimación, varias propiedades matemáticas y estadísticas de TR distribución (como cuantiles, momentos, una función que genera momentos, momentos condicionales, la tasa de peligro, la media vida residual, media vida pasada, la desviación media por media y mediana, organización stochastic, entropías varias, parámetros de tensión-fuerza y estadisticas de orden) están derivadas. Describimos brevemente los diferentes métodos de estimación, como máxima probabilidad, método de momentos, estimacién basada por percentil, mínimos cuadrados, método de máximos productos de espacios, el método de Cramér-von-Mises, los métodos de Anderson-Darling y right-tail Anderson-Darling, y compararlos con extensos estudios de simulaciones. Por último, la potencialidad del modelo está estudiando con dos conjuntos de datos reales. El margen de error, el promedio de error de las estimaciones y el percentage bootstrap de los confianza intervalos estan derivido por bootstrap remuestro

Epidemiology, clinical features, and impact of food habits on the risk of hepatocellular carcinoma: A case-control study in Bangladesh.

Hepatocellular carcinoma (HCC) is the sixth most common cancer and the third most common cause of cancer mortality worldwide. Infection with hepatitis B virus (HBV) and/or hepatitis C virus (HCV) is the most predominant cause of HCC. Concerns arise for the presence of additional risk factors, as there is still a large proportion of patients without HBV or HCV infection. Previous studies have reported that higher intake of fruits and vegetables and reduced consumption of red/processed meat might play a protective role in HCC etiology, though the nationwide proof is limited. Hence, we studied multiple risk factors including food habit, lifestyle, and clinical implications of HCC patients in Bangladeshi. Demographic, clinical, and biochemical data, as well as data on food habits, were collected in this study. Our results indicated that a high intake of rice (AOR 4.28, 95% CI 1.48 to 14.07, p = 0.011), low intake of fruits (AOR = 4.41 95% CI 1.48-15.46; p = 0.012), leafy vegetables (AOR = 2.80, 95% CI 1.32-6.08; p = 0.008), and fish (AOR = 4.64 95% CI 2.18-10.23; p<0.001) increased the HCC risk. Moreover, a high intake of eggs (AOR = 2.07 95% CI 0.98-4.43; p = 0.058) also showed an increased risk. Roti, non-leafy vegetables, red meat, and tea were found to have no association with HCC risk. This study revealed that food habit patterns and lifestyle may have a profound effect on HCC development among Bangladeshi patients in addition to well established risk factors

Age-related Risk Factors and Severity of SARS-CoV-2 Infection: a systematic review and meta-analysis

Objectives: We aimed to estimate the reported symptoms and comorbidities and assess the correlation between a series of symptoms and comorbidities and age of the patients’ positive in COVID-19. Methods: We performed a systematic review and meta-analysis [PROSPERO registration: CRD42020182677]. Databases [PubMed, SCOPUS, EMBASE, WHO, Semantic Scholar, and COVID-19 Primer] were searched for clinical studies published from January to April 2020. The pooled prevalence of symptoms and comorbidities were identified using the random effect model, and the multivariable factor analysis was performed to show the correlation between a group of symptoms and comorbidities and age of the COVID-19 patients. Results: Twenty-nine articles, with 4,884 COVID-19 patients were included in this study. &nbsp;Altogether, we found 33 symptoms and 44 comorbidities where the most frequent 19 symptoms and 11 comorbidities were included in the meta-analysis. The fever [84%], cough/dry cough [61%], and fatigue/weakness [42%] were found more prevalent. On the other hand, acute respiratory distress syndrome, hypertension and diabetes were the most prevalent comorbid condition. The multivariable factor analysis showed positive association between a group of symptoms and comorbidities, and with the patients' age. The symptoms comprising fever, dyspnea/shortness of breath, nausea, vomiting, abdominal pain, dizziness, anorexia and pharyngalgia; and the comorbidities including diabetes, hypertension, coronary heart disease, COPD/lung disease and ARDS were positively correlated with the COVID-19 patient’s age. Conclusion: As a unique effort, this study found a group of symptoms and comorbidities, correlated with age of the COVID-19 patients that may help to implement patient-centred interventions

Suicidal behaviors among undergraduate medical students in Bangladesh

Background: Suicide among medical students is a global public health concern; however, it is often addressed poorly in developing countries like Bangladesh. This study aims to examine suicidal behaviors among undergraduate medical students in Bangladesh. Methods: This cross-sectional analytical study was conducted between February and July of 2019. Data were collected from 583 MBBS students at Bangladesh’s public and private medical colleges. A convenience sampling method was used, and data were collected through a pretested semi-constructed questionnaire. Results: A lifetime suicidal ideation was found among 23.8% of the participants. Significant associations were found among lifetime suicidal ideation, plan and attempt with depression, comorbidity, and family history. Multivariable logistic regression models revealed that a family history of suicide attempts or death by suicide increased the odds six-fold for ideation, over sixfold for a plan, and threefold for an attempt. Females were twice likely to be susceptible to suicide ideation, plan, and attempt. Conclusion: Suicidality appears high among medical students in Bangladesh. Levels of depression, comorbidities, as well as substance abuse affect lifetime suicide ideation. A previous history of attempting or committing suicide in the respondent’s family increases the individual risk for ideation, plan, and attempt. Females are more vulnerable than males

Thalassemias in South Asia:clinical lessons learnt from Bangladesh

Abstract Thalassemias are emerging as a global public health concern. Due to remarkable success in the reduction of childhood mortality by controlling infectious diseases in developing countries, thalassemias are likely to be a major public health concern in the coming decades in South Asia. Despite the fact that Bangladesh lies in the world’s thalassemia belt, the information on different aspects (epidemiology, clinical course, mortality, complications and treatment outcomes) of thalassemias is lacking. In this comprehensive review, the aim is to to depict the epidemiological aspects of thalassemias, mutation profile and current treatment and management practices in the country by sharing the experience of dealing with 1178 cases over 2009–2014 time periods in a specialized thalassemia treatment centre. We have also discussed the preventative strategies of thalassemias from the context of Bangladesh which could be effective for other developing countries