Bounded-Bias Robust Estimation in Generalized Linear Latent Variable Models

This paper proposes a robust estimator for a general class of linear latent variable models (GLLVM) (Moustaki and Knott 2000, Bartholomew and Knott 1999). It is based on a weighted score function that is simple to implement numerically and is made consistent using the basic idea of indirect inference. The need of a robust estimator for these models is motivated by the study of the effect of model deviations such as data contamination on the maximum likelihood estimator (MLE). This is done with the use of the influence function (Hampel 1968, 1974) and the gross error sensitivity (Hampel, Ronchetti, Rousseeuw, and Stahel 1986). Simulation studies show that the MLE can be seriously biased by model deviations. The performance of the robust estimator in terms of bias and variance is compared to the MLE estimator with simulation studies and with a real example from a consumption survey.latent variable models, mixed items, influence function, robust estimation, indirect inference

Different Patterns of Association of Body Fat Percent and Body Mass Index with Pre-adolescent and Adolescent Asthma: a Cross-sectional Study Amongst Cypriot Schoolchildren

IEA-EEF European Congress of Epidemiology, Porto, Portugal, September 201

A forward search algorithm for detecting extreme study effects in network meta-analysis

In a quantitative synthesis of studies via meta-analysis, it is possible that some studies provide a markedly different relative treatment effect or have a large impact on the summary estimate and/or heterogeneity. Extreme study effects (outliers) can be detected visually with forest/funnel plots and by using statistical outlying detection methods. A forward search (FS) algorithm is a common outlying diagnostic tool recently extended to meta-analysis. FS starts by fitting the assumed model to a subset of the data which is gradually incremented by adding the remaining studies according to their closeness to the postulated data-generating model. At each step of the algorithm, parameter estimates, measures of fit (residuals, likelihood contributions), and test statistics are being monitored and their sharp changes are used as an indication for outliers. In this article, we extend the FS algorithm to network meta-analysis (NMA). In NMA, visualization of outliers is more challenging due to the multivariate nature of the data and the fact that studies contribute both directly and indirectly to the network estimates. Outliers are expected to contribute not only to heterogeneity but also to inconsistency, compromising the NMA results. The FS algorithm was applied to real and artificial networks of interventions that include outliers. We developed an R package (NMAoutlier) to allow replication and dissemination of the proposed method. We conclude that the FS algorithm is a visual diagnostic tool that helps to identify studies that are a potential source of heterogeneity and inconsistency

Alkaline phosphatase and its isoenzyme activity for the evaluation of bone metabolism in children receiving anticonvulsant monotherapy

AbstractThis study aimed to investigate whether carbamazepine, sodium valproate or phenobarbital as monotherapy in ambulatory epileptic children with adequate sun exposure have some effect on their bone metabolism based on the determination of total serum alkaline phosphatase (AP) levels and its bone isoenzyme activity. Blood samples were obtained from 118 epileptic children (37 on carbamazepine, 47 on sodium valproate and 34 on phenobarbital) and from corresponding healthy controls matched for age, gender and anthropometric parameters. AP and its liver, bone and intestinal isoenzyme levels, other common biochemical markers of bone and liver metabolism and drug levels were measured in the study participants. Patients on carbamazepine or phenobarbital had significantly elevated AP levels accompanied by increased bone and liver isoenzyme activity compared to controls. An increase of bone AP isoenzyme values, correlated with the duration of treatment ( r= 0.49, P= 0.002), was found in children on sodium valproate without, however, a concomitant significant elevation of total AP values. We conclude that children who receive antiepileptic drugs as monotherapy, even when residing in a Mediterranean country with adequate sunlight, may have their bone metabolism affected as indicated by the elevated levels of bone AP isoenzyme. This isoenzyme, but not total AP values, could therefore be used as a marker for the selection of patients who would be benefited by a thorough evaluation of their bone metabolism profile

Knowledge of Greek adolescents on human papilloma virus (HPV) and vaccination: A national epidemiologic study

Abstract: The aim of the present study was to identify the sexual behavior, attitudes, beliefs, and knowledge on sexually transmitted infections (STIs) focused on human papilloma virus (HPV) in the Greek adolescent population. The participants were 4547 adolescents, a representative sample for Greek territory with a mean age of 17 years. After written permission from Greek ministry of education each student completed a questionnaire with 36 questions. The fields covered were demographic characteristics, sexual life data, and basic knowledge on HPV. In the present study, 43% and 75% of the participants knew about HPV or cervical cancer, while more than 6 out of 10 did not know the association between the 2. More than 60% of the participants could not answer correctly neither about HPV infection and cervical cancer frequency in sexually active women, nor about protection methods against HPV and cervical cancer. This study shows that the low vaccination coverage of the Greek population may be due to lack of information and awareness of the adolescents and their parents. It is our duty to increase our efforts in order to better educate the population and vaccinate the population as early as possible in their reproductive years

Application of adipose-derived stromal cells in fat grafting: Basic science and literature review

Autologous fat is considered the ideal material for soft‑tissue augmentation in plastic and reconstructive surgery. The primary drawback of autologous fat grafting is the high resorption rate. The isolation of mesenchymal stem cells from adipose tissue inevitably led to research focusing on the study of combined transplantation of autologous fat and adipose derived stem cells (ADSCs) and introduced the theory of ʻcell‑assisted lipotransferʼ. Transplantation of ADSCs is a promising strategy, due to the high proliferative capacity of stem cells, their potential to induce paracrine signalling and ability to differentiate into adipocytes and vascular cells. The current study examined the literature for clinical and experimental studies on cell‑assisted lipotransfer to assess the efficacy of this novel technique when compared with traditional fat grafting. A total of 30 studies were included in the present review. The current study demonstrates that cell‑assisted lipotransfer has improved efficacy compared with conventional fat grafting. Despite relatively positive outcomes, further investigation is required to establish a consensus in cell‑assisted lipotransfer

Severe Jaundice in Two Children with Kawasaki Disease: A Possible Association with Gilbert Syndrome

Kawasaki disease is a systemic vasculitis, mainly encountered in children. It may affect any organ. Acute cholestasis and severe obstructive jaundice is an atypical manifestation of the disease. We herein present two children with Kawasaki disease and severe direct hypebilibirunemia who also were homozygous and heterozygous respectively for the (TA)7 promoter polymorphism of Gilbert syndrome. Intravenous immunoglobulin was administered to both patients at the acute phase of the disease and the fever remitted within 24 hr following the immunoglobulin administration. Furthermore oral aspirin at a dose of 80-100 mg/kg/24 hr was also given. The first child did not develop any coronary ectasia or aneurysm, whereas dilation of the right coronary artery was identified in the second child, one month after the disease onset. We discuss the possible contribution of Gilbert syndrome to the development of jaundice in our patients

Robust Estimation and Inference for Generalised Latent Trait Models

The paper discusses the effect of model deviations such as data contamination on the maximum likelihood estimator (MLE) for a general class of latent trait models (citeNP{MoKn:00}). This is done with the use of the influence function (Hampel 1968, 1974) a mathematical tool to assess the robustness properties of any statistic, such as an estimator. Simulation studies show that the MLE can be seriously biased by model deviations. Therefore, we then propose alternative robust estimators that are not less influenced by data contamination. The performance of the robust estimators in terms of bias and variance is compared to the MLE estimator both analytically and through simulation studies

The Current Practice of Noninvasive Ventilation in Patients With Cystic Fibrosis

In patients with cystic fibrosis (CF), despite the availability of many different pharmacologic agents, lung function deteriorates and lung disease progresses and leads to hypercapnic respiratory failure in some patients. In such cases, noninvasive ventilation (NIV) seems to be a promising technique that can be used on demand. This review summarizes the current applications of NIV in clinical settings as well as findings of the clinical trials that involved the delivery of NIV on variable occasions, such as an adjunct to physiotherapy, in nocturnal hypoventilation, and acute and chronic respiratory failure. NIV has been used in patients with CF and with advanced lung disease who are not considered candidates for lung transplantation. It can stabilize lung function, although its effect on hypercapnia is not always evident. Nocturnal NIV has been used in patients with CF and with hypoventilation during sleep but without clear benefits on daytime P-CO2. NIV as an adjunct to chest physiotherapy may be helpful when desaturation is observed during physiotherapy and when there are signs of respiratory muscle fatigue. NIV use in CF has been increasing, mainly in adult CF centers, and offers patients an opportunity to reach lung transplantation or to overcome acute hypercapnic respiratory failure

Bounded-Bias Robust Estimation in Generalized Linear Latent Variable Models

This paper proposes a robust estimator for a general class of linear latent variable models (GLLVM) (Moustaki and Knott 2000, Bartholomew and Knott 1999). It is based on a weighted score function that is simple to implement numerically and is made consistent using the basic idea of indirect inference. The need of a robust estimator for these models is motivated by the study of the effect of model deviations such as data contamination on the maximum likelihood estimator (MLE). This is done with the use of the influence function (Hampel 1968, 1974) and the gross error sensitivity (Hampel, Ronchetti, Rousseeuw, and Stahel 1986). Simulation studies show that the MLE can be seriously biased by model deviations. The performance of the robust estimator in terms of bias and variance is compared to the MLE estimator with simulation studies and with a real example from a consumption survey