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Robust and Bootstrap Procedures in Regression Analysis and Outliers Detection Tests

Thesis Info

Access Option

External Link

Program

PhD

Institute

University of Peshawar

City

Peshawar

Province

KPK

Country

Pakistan

Thesis Completing Year

2013

Thesis Completion Status

Completed

Subject

Mathemaics

Language

English

Link

http://prr.hec.gov.pk/jspui/handle/123456789/885

Added

2021-02-17 19:49:13

Modified

2024-03-24 20:25:49

ARI ID

1676727106885

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It is evident from the comments by Bernoulli (1777) that the history of outliers is very old and traces back to some 200 years ago indicating that “discardin g discordant observations” was a common practice even 200 years ago. In the opinion of investigator, “Outliers” are the observations that deviate from the remaining observations or bulk of the data and require proper treatment as statistical anal yses are h ighl y influenced by the presence of such observation in all t ypes of data sets. Many attempts have been made to cope with such observations and to provide protection against outliers. Robust statistics and robust regression techniques have been developed b y researchers with the passage of time to handle outliers and to minimize the effect of outliers. Work is still continuing to modify the previousl y devel oped techniques or to introduce even more advanced and improved techniques. Our present study has thre e important dimensions. The first portion of this study deals with the comparison of several tests developed by researchers to identify one or more outliers in single sample case. In this study we also propose some univarite tests to be used for the detection of outliers in case of sampling from a heavy tailed symmetric distribution, that is, Cauchy distribution. We conduct detailed simulation studies to compute critical values for the tests for various sample sizes available in the literature and also for the proposed tests while sampling is from the Cauchy distribution. We also have computed simulated powers based on 10000 simulations to compare iithese tests for various sample sizes up to 30 in the presence of different number of outliers varying from 1 to 5. We consider three (3) examples where artificial data sets were generated from Cauchy distribution containing 1, 2 and 3 outliers to investigate the performance of all of the tests under consideration. The second part of m y PhD thesis is mainl y concerne d with robust regression. Several researchers have proposed M - estimators and redescending M- estimators to handle outliers by assigning smaller weights to outliers in order to minimize their effect. We propose a new and efficient redescending M - estimator, called “Alamgir Redescending M- Estimator (ALARM)”. We investigate its asymptotic efficiency for various sample sizes and different number of predictors. We determine the optimum value for the tuning constant parameter of our proposed estimator. We condu cted simulation studies to evaluate and compare its performance with several other redescending M - estimators available in the literature. Our proposed estimator performs better than rest of the estimators in majorit y of simulated scenarios and outperforms the remaining estimators in some cases, particularl y, in the prese nce of higher percentages of ou tliers in the data. We also present some examples based on real data sets to illustrate the performance of our proposed estimator. The proposed estimator does well in fitting the real data sets containing different percentages of outliers and detected as many outliers as any other estimator did. Our proposed estimator provides protection against outliers and proves to be very efficient estimator. iiiIn the last pa rt of my PhD thesis, we propose a new bootstrap procedure, called “ Split Sample Bootstrap (SSB)” which is a very robust alternative to other classical or recentl y developed bootstrap procedure providing maximum protection against outliers. The proposed pro cedure has high breakdown point. We conduct ed some simulation studies to examine the performance of SSB and to compare it with two other bootstrap procedures under various simulation scenarios. The performance of the proposed procedure and the two other procedures is judged by computing the bootstrap estimate of the bias, bootstrap standard error (SE) and length of the bootstrap confidence interval. We observe very promising results for our proposed procedure with respect to bias, SE and length. Our propose d bootstrap procedure result s in numerical stabilit y and high efficiency of the estimates as compared to other two bootstrap procedures. The proposed procedure result in shortest confidence intervals for the parameter estimates for all sample sizes and for different number of predictor variables in the regression model at all level of contaminations, particularl y, in the presence of higher percentage of outliers as compared to the other two bootstrap procedures under consideration in the study. We consider two real data examples and the results similar to simulation results have been found in both examples. The Computer programing for simulation studies was done in R software (version 2.14.1 ).
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معاشرتی رویوں کا شعری اظہار

معاشرتی رویوں کا شعری اظہار

تائب نظامی کا بچپن ہی سے حجرۂ صابری سے تعلق ہے۔ بنابریں میں ان کو اور ان کی شاعری کے مزاج کو بخوبی سمجھتا ہوں۔ ان کے عجز نے ان کی شخصیت اور سہل ممتنع میں شاعری نے ان کو ممتاز شعرا کی صف میں کھڑا کر دیا ہے۔
ان کی شاعری میں غمِ جاناں کے ساتھ ساتھ غمِ دوراں کا بھی بھرپور تذکرہ موجود ہے۔ خارجی اور داخلی جذبات و احساسات کو بھی بڑے خوب صورت انداز میں موضوعِ سخن بنایا گیا ہے۔
ایک شاعر کو معاشرے کے جن رویوں کا علم ہونا چاہیے اُن رویوں کا تائب نظامی کو بدرجہ احسن ادراک ہے۔ دعا گو ہوں کہ ان کا پہلا شعری مجموعہ ’’صبحِ قفس‘‘ مقبولِ خواص و عوام ہو۔ نمونے کے طور پر ان کا ایک شعر ملاحظہ ہو:
ہر صبح مری صبح قفس جیسی ہے تائب
ہر شام مری شامِ غریباں کی طرح

دیوان تنویر نوازش صابری
حجرہ صابری
تاندلیا نوالہ

Phase-dependent expression profiling and quantification of several growth factors in liver regeneration after partial hepatectomy

Growth factors are the potential operational members which control different phases of liver regeneration. Different growth factors have expression regulation in the whole process relating to different phases of liver regeneration. Objective: To assess the expression regulation of different growth factors and cytokines involved in liver regeneration in a phase-dependent manner. Methods: Blood and liver samples were collected and analyzed on 1st, 3rd, 5th, 7th and 14th postoperative days after 50% Partia hepatectomy (PHx). Results: Steady increase of liver regeneration rate was recorded from 90.8% (1st day) to 97.9% (7th day). Liver function tests further confirmed the steady liver recovery in PHx mice. Several growth factors such as HGF and VEGF exhibited an up-regulation till 5th day and later gradual decrease till 14th day compared to control mice. Albumin, CK18 and CK19 showed sequential expression increase from 1st to 14th day compared to AFP and HNF-4α upregulated until 5th and 1st day, respectively. Quantification of these growth factors further confirm our results. Conclusions: Conclusively, these results highlight a phase-dependent regulation and role of growth factors in liver regeneration and recovery

Biochemical Attributes of Essential Oils from Selected Medicinal Herbs Grown in Different Agroclimatic Regions of Pakistan

Essential oils are plant‘s secondary metabolites that are known for their fragrance and food flavour properties.These odoriferous oils offer a promising potential for multiple applications such as in the fields of agriculture, food, cosmetics, medicine, pharmaceutical industry and aromatherapy. Chemistry and biological attributes of essential oils are deemed to be varied not only among different varieties of the same plant speciesnevertheless different agro-climatic conditions also affect the biochemical composition of the oils due to morphological diversity of the plants.In the present dissertation, selected medicinal herbs such as Mentha spicata, Menthapiperitta, O.basilicum Lamiaceae] andC.citratus[Poaceae], harvested from different geographicalzones of Punjab, Pakistan, were evaluated for yield, physicochemical and biological potential of their oils which were produced by two different methods including hdrodistillation (HD) and supercritical fluid extraction (SCFE). Gas chromatography attached with flame ionization detector (FID) and Gas chromatography fitted with mass spectrometry (MS)analyses of chemical costituents of volatile oils showed the presence of different types of oxygenated monoterpene (OM), monoterpene hydrocarbon (MH), sesquiterpene hydrocarbon (SH), oxygenated sesquiterpene (OS) and phenyl propanoid (PP).Depending upon the isolation mode, the tested essential oils exhibited a promising extent of antioxidant and antimicrobial and hemolytic activities, total phenolics and total flavonoids contents.With respect to different harvesting such as drought stressed, hilly, arid and irrigated regions, the tested essential oils revealed considerable differences in yield, chemical composition, TPC, TFC and biological properties that can be linked to varying agro-ecological parameters of the regions under study.Generally, the essential oilsextracted from the drought stressed region leave samples presented superior antimicrobial and hemolytic actions while,samples from hilly regions exhibited a greater range of antioxidant potential and total phenolics and flavonoids. A significant variation noted in the percentage yield,volatiles chemical composition and biological properties/actionscan be related to theirvariable chemical profiling resulted from morphologicaldiversity of the plants.