Search results for "sampling"

Saliva: Its value as a biological matrix and current methods of sampling

2006

Saliva is a non-invasive medium, its analysis is useful to measure a wide range of hormones, drugs, narcotics, antibodies, host, microbial, fungal and viral DNA up to salivary mRNA; hence, it has been suggested to be an easy and reliable biomarker in disease diagnostics, such as inflammatory mouth infections/diseases, and in normal health surveillance. In light of this potential, our primary endpoint is to review the current knowledge on saliva analyses and its recent methods of sampling.

Stagewise pseudo-value regression for time-varying effects on the cumulative incidence

2015

In a competing risks setting, the cumulative incidence of an event of interest describes the absolute risk for this event as a function of time. For regression analysis, one can either choose to model all competing events by separate cause-specific hazard models or directly model the association between covariates and the cumulative incidence of one of the events. With a suitable link function, direct regression models allow for a straightforward interpretation of covariate effects on the cumulative incidence. In practice, where data can be right-censored, these regression models are implemented using a pseudo-value approach. For a grid of time points, the possibly unobserved binary event s…

Pitfalls of hypothesis tests and model selection on bootstrap samples: Causes and consequences in biometrical applications

2015

The bootstrap method has become a widely used tool applied in diverse areas where results based on asymptotic theory are scarce. It can be applied, for example, for assessing the variance of a statistic, a quantile of interest or for significance testing by resampling from the null hypothesis. Recently, some approaches have been proposed in the biometrical field where hypothesis testing or model selection is performed on a bootstrap sample as if it were the original sample. P-values computed from bootstrap samples have been used, for example, in the statistics and bioinformatics literature for ranking genes with respect to their differential expression, for estimating the variability of p-v…

A widely used sampling device in colorectal cancer screening programmes allows for large-scale microbiome studies.

2018

We read with interest the article by Passamonti et al ,1 reporting the performance of two different faecal immunochemical tests (FITs) highlighting the importance of standardisation and validation of screening methodologies. Conventionally, laboratory-based FIT is the preferred approach in testing for occult blood in faeces, which includes colorectal cancer screening programmes.2–4 The potential of preserving stable faecal samples in a widely used FIT buffer for microbiome research would enable prospective microbiome studies in generally healthy subjects undergoing colorectal cancer screening. For this purpose, we evaluated faecal sample stability in the commonly used OC-Sensor (Eiken Chemi…

Is there any therapeutic role of pelvic and para-aortic lymphadenectomy in apparent early stage epithelial ovarian cancer?

2020

Objective: The therapeutic role of pelvic and para-aortic lymphadenectomy in surgical staging of apparent early-stage epithelial ovarian cancer (eEOC) is still under debate. The aim of this study was to evaluate the potential therapeutic role of systematic lymphadenectomy in patients with eEOC. Methods: Multi-center retrospective cohort study, comparing women with apparent eEOC who underwent comprehensive bilateral pelvic and para-aortic lymphadenectomy (defined as ≥20 lymph nodes) versus patients receiving no lymphadenectomy or lymph node sampling, from 05/1985 to 12/2016. Patients with bulky nodes at CT-scan and those without complete intra-peritoneal surgical staging were excluded. Only …

Higher education instructors' intention to use educational video games: an fsQCA approach

2019

Educational video games (EVGs) offer instructors a myriad of opportunities to motivate and engage students in the learning process. Nevertheless, instructors can be influenced by barriers that prevent them from using EVGs in their courses (e.g. lack of expertise with EVGs). Instructors can also be influenced by different drivers that might increase their intention to use EVGs. This research analyses the effects of four variables (perceived usefulness, perceived ease of use, attention, and relevance) as factors contributing or preventing the use of EVGs by instructors serving in Higher Education institutions. Data of 170 instructors, who were surveyed through an online questionnaire using a …

2019

Background The SCL-K-9 is the latest short version of the multidimensional Symptom-Checklist 90-R. Up to now, its psychometric properties have not been clarified sufficiently as the nine items have not yet been presented exclusively in a representative sample. Therefore, psychometric properties, model fit values as well as norm-values were analyzed. Methods For the sample, N = 2,507 participants aged 14 to 92, n = 1,379 women and n = 1,128 men, and a mean age of 48.79 (SD = 17.91), were selected from the general population by random-route sampling. Confirmatory factor analyses applying full information maximum likelihood (FIML) tested the model fit. The reliability estimations and effect si…

Seasonal variations of leaf area index of agricultural fields retrieved from Landsat data

2008

Abstract The derivation of leaf area index (LAI) from satellite optical data has been the subject of a large amount of work. In contrast, few papers have addressed the effective model inversion of high resolution satellite images for a complete series of data for the various crop species in a given region. The present study is focused on the assessment of a LAI model inversion approach applied to multitemporal optical data, over an agricultural region having various crop types with different crop calendars. Both the inversion approach and data sources are chosen because of their wide use. Crops in the study region (Barrax, Castilla–La Mancha, Spain) include: cereal, corn, alfalfa, sugar bee…

Random resampling numerical simulations applied to a SEIR compartmental model

2021

AbstractIn this paper, we apply resampling techniques to a modified compartmental SEIR model which takes into account the existence of undetected infected people in an epidemic. In particular, we implement numerical simulations for the evolution of the first wave of the COVID-19 pandemic in Spain in 2020. We show, by using suitable measures of goodness, that the point estimates obtained by the bootstrap samples improve the ones of the original data. For example, the relative error of detected currently infected people is equal to 0.061 for the initial estimates, while it is reduced to 0.0538 for the mean over all bootstrap estimated series.

Coupled conditional backward sampling particle filter

2020

The conditional particle filter (CPF) is a promising algorithm for general hidden Markov model smoothing. Empirical evidence suggests that the variant of CPF with backward sampling (CBPF) performs well even with long time series. Previous theoretical results have not been able to demonstrate the improvement brought by backward sampling, whereas we provide rates showing that CBPF can remain effective with a fixed number of particles independent of the time horizon. Our result is based on analysis of a new coupling of two CBPFs, the coupled conditional backward sampling particle filter (CCBPF). We show that CCBPF has good stability properties in the sense that with fixed number of particles, …