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Effects of Bayesian Model Selection on Frequentist Performances: An Alternative Approach

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Applied Mathematics 2016年第10期7卷 1103-1115页

It is quite common in statistical modeling to select a model and make inference as if the model had been known in advance;i.e. ignoring model selection uncertainty. The resulted estimator is called post-model selection estimator (PMSE) whose properties are hard to derive. Conditioning on data at hand (as it is usually the case), Bayesian model selection is free of this phenomenon. This paper is concerned with the properties of Bayesian estimator obtained after model selection when the frequentist (long run) performances of the resulted Bayesian estimator are of interest. The proposed method, using Bayesian decision theory, is based on the well known Bayesian model averaging (BMA)’s machinery;and outperforms PMSE and BMA. It is shown that if the unconditional model selection probability is equal to model prior, then the proposed approach reduces BMA. The method is illustrated using Bernoulli trials.

关键词： Model Selection Uncertainty Model Uncertainty Bayesian Model Selection Bayesian Model Averaging Bayesian Theory Frequentist Performance

Frequentist Model Averaging and Applications to Bernoulli Trials

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Open Journal of Statistics 2016年第3期6卷 545-553页

作者： georges nguefack-tsague Walter Zucchini Siméon Fotso Biostatistics Unit Department of Public Health Faculty of Medicine and Biomedical Sciences University of Yaounde 1 Yaounde Cameroon Institute for Statistics and Econometrics University of Goettingen Goettingen Germany Department of Mathematics Higher Teachers’ Training College University of Yaoundé I Yaoundé Cameroon

In several instances of statistical practice, it is not uncommon to use the same data for both model selection and inference, without taking account of the variability induced by model selection step. This is usually referred to as post-model selection inference. The shortcomings of such practice are widely recognized, finding a general solution is extremely challenging. We propose a model averaging alternative consisting on taking into account model selection probability and the like-lihood in assigning the weights. The approach is applied to Bernoulli trials and outperforms Akaike weights model averaging and post-model selection estimators.

关键词： Model Selection Post-Model Selection Estimator Frequentist Model Averaging Bernoulli Trials

Missed Opportunities for Vaccination and Associated Factors among Children Aged 12 - 23 Months in Cameroon: Further Analyses of 2018 Cameroon Demographic and Health Survey

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Health 2022年第10期14卷 1081-1103页

作者： Solange Whegang Youdom Diomède Njinkui Noukeu georges nguefack-tsague Jerôme Ateudjieu Department of Public Health Faculty of Medicine and Pharmaceutical Sciences University of Dschang Dschang Cameroon Department of Public Health Faculty of Medicine and Biomedical Sciences University of Yaoundé 1 Yaoundé Cameroon Division of Health Operations Research Ministry of Public Health Yaoundé Cameroon

Background: Low vaccination coverage has been attributed to missed opportunities for vaccination (MOV). This study examines the prevalence of MOV, and its associated factors among children in Cameroon. Methods: Data from the 2018 Demographic and Health Survey (DHS) was analyzed for children with at least one vaccination date in the home-based record (HBR). Immunization performances such as accessibility, drop-out, and timeliness, were assessed. Service quality was assessed using MOV. Multiple logistic regression examined the effect of DHS variables on MOV outcomes, and a decision tree approach was used to study their interaction. Results: Overall, 1824 children aged 12 to 23 months were surveyed;1285 (70.45%) had cards seen with vaccination dates leading to 85.03% of immunization activities. A proportion of 46.5% of children were not completely vaccinated. There was 27% of drop-out between BCG and MCV1, and less than 10% with the specific antigens. Vaccination timeliness proportions ranged from 42.18% for BGC to less than 70% for PENTA1-3. The national prevalence of MOV for simultaneous vaccines was 75.1% (95% confidence interval (CI) = 72;79). Among those who experienced MOV, 67.4% (95% CI = 60 - 73) were uncorrected MOV. MOV was an issue in all regions and comparable in rural areas that urban areas (p = 0.2). Dose-specific MOV ranged from 2.66% (for the third dose of the pneumococcal conjugate vaccine) to 91.12 (for the yellow fever vaccine). Second birth order children experienced more MOV than first born children (adjusted odds ratio (aOR) = 1.67, 95% CI: 1.11 - 2.47). Children born to non-educated/primary level mothers had increased odds of experiencing a MOV than those born to educated mothers (aOR = 1.48, 95% CI = 1.007 - 2.19/aOR = 1.55, 95% CI = 1.12 - 2.09). Children from poorest households were at high risk of experiencing MOV for any vaccine than richest households (aOR = 2.04, 95% CI = 1.11 - 3.76). Conclusion: There is a burden of MOV and under immuniz

关键词： Missed Opportunity Cameroon Demographic and Health Survey Global Health Vaccination Date MOV Simultaneous Vaccines

State of Play of the Use of Children’s Health Booklets in Cameroon according to Child Health Professionals

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Open Journal of Pediatrics 2022年第4期12卷 688-710页

作者： Collins Tchakoute Félicitée nguefack Anicet Romaric Mpangop David Chelo Yolande Djike Puepi Fokam georges nguefack-tsague Centre Médical la Cathédrale Yaoundé Cameroon Centre Médical la Cathédrale Yaoundé Cameroon Faculty of Medicine and Biomedical Sciences University of Yaoundé 1 Yaoundé Cameroon AfricanGenesic Health Medical and Surgical Centre Yaoundé Cameroon Centre Mèreet Enfant of the Chantal Biya Foundation Yaoundé Cameroon Faculty of Health Sciences University of Buea Buea Cameroon

Introduction: The Child health booklet has been shown to be an essential tool for monitoring the implementation of interventions with a high impact on reducing infant and child mortality. Objective: To describe the opinion of child health providers about child health records. Methodology: Cross-sectional survey of health professionals on content, ease of use and recommendations for a health record of the ideal child. Results: About 3/4 (75%) of participants considered medical follow-up useful and 91.5% wanted it to be conducted at all levels of health care. According to 93% of them, all health care providers should be involved. However, almost two-thirds (65.5%) had never been trained to use the child’s health record. About half (54.2%) of them had already seen the national manual and only 43.7% had ever filled it out, 82.2% of whom found it very difficult. With regards to the assessment of the content, 44.4% to 57.7% of respondents were dissatisfied with 12 of the 16 subheadings of the handbook. As for an ideal child health record, the majority recommended that it should contain indicators related to: childbirth, growth, monitoring of preventive activities and advice to parents. Conclusion: Child health booklets available in health facilities in Cameroon are not optimally used to reduce infant and child morbidity and mortality. It is important to review the content of the child’s health booklets in order to adapt it to the Cameroonian context.

关键词： Booklets Health Child Use Opinion Providers

Growth and Associated Factors in Children and Adolescents Living with HIV/AIDS Followed at the Mother and Child Centre of the Chantal Biya Foundation, Yaoundé-Cameroon: A Case Control Study

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Open Journal of Pediatrics 2020年第1期10卷 194-205页

作者： David Chelo Eulalie Landrine Moguon Fondjo Pierre Fotsing Kwetche Séraphin nguefack Félicitée nguefack Suzanne Ngo Um georges nguefack tsague Mother and Child Centre Chantal BIYA Foundation Yaoundé Cameroon Department of Pediatrics Faculty of Medicine and Biomedical Sciences University of Yaoundé 1 Yaoundé Cameroon Faculty of Health Sciences Banganté Cameroon Gyneco-Obstetric and Pediatric Hospital Yaoundé Cameroon Department of Public Health Faculty of Medicine and Biomedical Sciences University of Yaoundé 1 Yaoundé Cameroon

Background: HIV/AIDS has a negative impact on child growth. Assessing the growth of infected children is an important part of the overall care of these children which in turn improves the monitoring and prognosis of the disease. The purpose of the study was to describe and compare the growth of children living with HIV with those not infected and to identify the associated factors. Method: This was an analytical case control study conducted in a pediatric hospital, Yaoundé from January 25th to June 20th 2019. Our study population consisted of 164 children with an age range from 06 weeks to 19 years old of which we had 41 HIV-infected cases and 123 uninfected controls matched by sex and age plus or minus 02 months. Anthropometric parameters were measured according to the standards described by the WHO. The data was entered and analyzed using Epi info 3.5.4, WHO Anthro and WHO Anthropoplus softwares. The chi-square and the Fisher’s exact tests were used to compare qualitative variables, with a significance threshold set at P less than 5%. Results: Of the 41 cases, 15 (36.6%) had at least one anthropometric index (weight for age, height for age, weight for height) -2 Z score versus 05 for controls (4.1%). 36.6% of cases had growth retardation (Height for age -2 Z score) compared to 4.1% in controls with a significant difference (p = 0.000). In 18.2% of cases, underweight was found (Weight for age -2 Z score) with a significant difference compared to controls (p = 0.000). Wasting was present in 10% of infected children (P = 0.240). We found 7.3% obesity/overweight in cases and 25.2% in controls (P = 0.003). We did not find any associated factor with growth disorders in our study. Conclusion: Infected children are smaller in weight and size. After multivariate analysis, there remained a significant difference between cases and controls regarding stunting, obesity and overweight. No factors studied were associated with the growth disorders detected, which suggests that gr

关键词： Growth HIV/AIDS Child Adolescent Yaoundé

Inter-Observer Variability in the Detection and Interpretation of Chest X-Ray Anomalies in Adults in an Endemic Tuberculosis Area

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Open Journal of Medical Imaging 2015年第3期5卷 143-149页

作者： Boniface Moifo Eric Walter Pefura-Yone georges nguefack-tsague Marie Laure Gharingam Jean Roger Moulion Tapouh André-Pascal Kengne Samuel Nko’o Amvene Faculty of Medicine and Biomedical Sciences (FMBS) The University of Yaoundé I Yaoundé Cameroon Department of Radiology and Radiation Oncology FMBS Yaoundé Cameroon Department of Internal Medicine and Specialties’ FMBS Yaoundé Cameroon Service of Pneumology A Jamot Hospital of Yaoundé Yaoundé Cameroon Department of Public Health FMBS Yaoundé Cameroon South African Medical Research Council & University of Cape Town Cape Town South Africa

Purpose: To assess the inter-observer agreement in reading adults chest radiographs (CXR) and determine the effectiveness of observers in radiographic diagnosis of pulmonary tuberculosis (PTB) in a tuberculosis endemic area. Methods: A quasi-observational study was conducted in the Pneumology Department of Yaounde Jamot Hospital (Cameroon) from January to March 2014. This included six observers (two chest physicians, two radiologists, two end-training residents in medical imaging) and 47 frontal CXRs (4 of diffuse interstitial lung disease, 6 normal, 7 of lung cancers, 7 of bacterial pneumonia, 23 of PTB). The sample size was calculated on the basis of an expected 0.47 Kappa with a spread of 0.13 (α = 5%, CI = 95%) for six observers and five diagnostic items. The analysis of concordance was focused on the detection of nodules, cavitary lesions, pleural effusion, adenomegaly and diagnosis of PTB and lung cancer. These intervals of kappa coefficient were considered: discordance (0.81). Results: The average score for the detection of caverns was the highest (58.3%) followed by that of the correct diagnosis of tuberculosis (49.3%). Pneumologists had the highest proportions of correct diagnosis of tuberculosis (69.6% and 73.9%) and better inter-observer agreement (k = 0.71) for PTB diagnosis. Observers were more in agreement for the detection of nodules (0.32 - 0.74), adenomegalies (0.43 - 0.69), and for the diagnosis of cancer (0.22 - 1) than for the diagnosis of tuberculosis (0.19 - 0.71). Disagreements were more frequent for the detection of pleural effusions (-0.08 - 0.73). Conclusion: The inter-observer agreement varies with the type of lesions and diagnosis. Pneumologists were most effective for the diagnosis of pulmonary tuberculosis. Observers were more in agreement for the detection of nodules and the diagnosis of cancer than for the diagnosis of pulmonary tuberculosis.

关键词： Inter-Observer Variability Concordance Pulmonary Tuberculosis Nodules Caverns Lung Cancer Chest Radiography Kappa

Impact of Standardized Scheme on the Detection of Chest X-Ray Abnormalities and Radiographic Diagnosis of Pulmonary Tuberculosis in Adult

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Open Journal of Medical Imaging 2014年第1期4卷 23-30页

作者： Marie Laure Gharingam Boniface Moifo Eric Walter Pefura Yone André Pascal Kengne Jean Roger Moulion Tapouh Annick Laure Edzimbi georges nguefack-tsague Samuel Nko’o Amvene Department of Medical Imaging and Radiation Therapy The University of Yaoundé I Yaoundé Cameroon Faculty of Medicine and Biomedical Sciences The University of Yaoundé I Yaounde Cameroon Faculty of Medicine and Biomedical Sciences The University of Yaoundé I Yaounde Cameroon Department of Internal Medicine and Specialties The University of Yaoundé I Yaoundé Cameroon Service of Pulmonology Yaounde Jamot Hospital Yaounde Cameroon Faculty of Medicine and Biomedical Sciences The University of Yaoundé I Yaounde Cameroon Department of Medical Imaging and Radiation Therapy The University of Yaoundé I Yaoundé Cameroon Faculty of Medicine and Biomedical Sciences The University of Yaoundé I Yaounde Cameroon Department of Public Health The University of Yaoundé I Yaoundé Cameroon South African Medical Research Council & University of Cape Town Cape Town South Africa

Purpose: The complexity of chest radiography (CXR) is a source of variability in its interpretation. We assessed the effect of an interpretation grid on the detection of CXR anomalies and radio- graphic diagnosis of tuberculosis in an endemic area for tuberculosis. Methods: The study was conducted in Yaounde (Cameroon). Six observers (2 pulmonologists, 2 radiologists and 2 senior residents in medical imaging) interpreted 47 frontal CXR twice two months apart without (R1) and with (R2) the aid of an interpretation grid. We focused on the detection of micro nodules (n = 16), cavitations (n = 12), pleural effusion (n = 6), adenomegaly (n = 6), and diagnosis of tuberculosis (n = 23) and cancer (n = 7). Results: The average score for accurate detection of elementary lesions was 40.4% [95%CI: 25% - 58.3%] in R1 and 52.1% [36.9% - 65.3%] in R2. The highest im- provement was observed for micro nodules (19.8%). Cavitations had the highest proportions of accurate detections (58.3% in R1 and 65.3% in R2). The average score of accurate diagnosis was 46.1% in R1 and 57.4% in R2. Accurate diagnosis improved by 3.6% for tuberculosis and 19% for cancer between R1 and R2. Intra-observer agreement was higher for the diagnosis of cancers (0.22 ≤ k ≤ 1) than for diagnosing tuberculosis (0.21 ≤ k ≤ 0.68). Inter-observer agreement was highly variable with a modest improvement for the diagnosis of tuberculosis in R2. Conclusion: Standardized interpretation scheme improved the detection of CXR anomalies and diagnosis of tuberculosis. It significantly improved inter-observer’s agreement in diagnosing tuberculosis but not in detecting most lesions.

关键词： Chest Radiography Interpretation Scheme Tuberculosis Micro Nodules Cavitations Agreement

Missed Opportunities for Vaccination and Associated Factors among Children Aged 12 - 23 Months in Cameroon: Further Analyses of 2018 Cameroon Demographic and Health Survey

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State of Play of the Use of Children’s Health Booklets in Cameroon according to Child Health Professionals

Health 2022年第10期

作者： solange whegang youdom diomède njinkui noukeu georges nguefack-tsague jerôme ateudjieu

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