Sensitivity and specificity of normality tests and consequences on reference interval accuracy at small sample size: a computer-simulation study

2016 ◽  
Vol 45 (4) ◽  
pp. 648-656 ◽  
Author(s):  
Kevin Le Boedec
Keyword(s):  
Computer Simulation ◽  
Sample Size ◽  
Sensitivity And Specificity ◽  
Simulation Study ◽  
Small Sample Size ◽  
Reference Interval ◽  
Small Sample ◽  
Computer Simulation Study

scholarly journals Regression shrinkage methods for clinical prediction models do not guarantee improved performance: Simulation study

2020 ◽  
Vol 29 (11) ◽  
pp. 3166-3178 ◽  
Author(s):  
Ben Van Calster ◽  
Maarten van Smeden ◽  
Bavo De Cock ◽  
Ewout W Steyerberg
Keyword(s):  
Maximum Likelihood ◽  
Sample Size ◽  
Simulation Study ◽  
Prediction Models ◽  
Small Sample Size ◽  
Predictive Performance ◽  
Small Sample ◽  
Adaptive Lasso ◽  
Shrinkage Methods ◽  
Improved Performance

When developing risk prediction models on datasets with limited sample size, shrinkage methods are recommended. Earlier studies showed that shrinkage results in better predictive performance on average. This simulation study aimed to investigate the variability of regression shrinkage on predictive performance for a binary outcome. We compared standard maximum likelihood with the following shrinkage methods: uniform shrinkage (likelihood-based and bootstrap-based), penalized maximum likelihood (ridge) methods, LASSO logistic regression, adaptive LASSO, and Firth’s correction. In the simulation study, we varied the number of predictors and their strength, the correlation between predictors, the event rate of the outcome, and the events per variable. In terms of results, we focused on the calibration slope. The slope indicates whether risk predictions are too extreme (slope < 1) or not extreme enough (slope > 1). The results can be summarized into three main findings. First, shrinkage improved calibration slopes on average. Second, the between-sample variability of calibration slopes was often increased relative to maximum likelihood. In contrast to other shrinkage approaches, Firth’s correction had a small shrinkage effect but showed low variability. Third, the correlation between the estimated shrinkage and the optimal shrinkage to remove overfitting was typically negative, with Firth’s correction as the exception. We conclude that, despite improved performance on average, shrinkage often worked poorly in individual datasets, in particular when it was most needed. The results imply that shrinkage methods do not solve problems associated with small sample size or low number of events per variable.

scholarly journals A CRITICAL EXAMINATION OF THE USE OF THE JOLICOEUR-BRUNEL DIAGRAMS TO DEMONSTRATE SELECTION IN BIOLOGICAL POPULATIONS

Genetics ◽  
1972 ◽  
Vol 70 (1) ◽  
pp. 181-185
Author(s):  
David Wool
Keyword(s):  
Computer Simulation ◽  
Sample Size ◽  
Simulation Study ◽  
Critical Examination ◽  
Genetic Composition ◽  
Computer Simulation Study

ABSTRACT The use of the Jolicoeur-Brunel hexagonal diagrams to demonstrate selection in biological populations was tested in a computer-simulation study.—The results show convincingly that the probabilities associated with the six deviation patterns illustrated in the hexagonal diagrams are not equal, but depend on the sample size and in particular on the genetic composition of the sampled population. The diagrams thus cannot be used to demonstrate selection, but only to illustrate trends of deviation patterns, which may be real biologically.

Application of Ultrasound Elastography for Assessing Intestinal Fibrosis in Inflammatory Bowel Disease: Fiction or Reality?

2020 ◽  
Vol 21 ◽  
Author(s):  
Roberto Gabbiadini ◽  
Eirini Zacharopoulou ◽  
Federica Furfaro ◽  
Vincenzo Craviotto ◽  
Alessandra Zilli ◽  
...  
Keyword(s):  
Inflammatory Bowel Disease ◽  
Sample Size ◽  
Bowel Disease ◽  
Small Sample Size ◽  
Shear Wave Elastography ◽  
Small Sample ◽  
Ultrasound Elastography ◽  
Invasive Technique ◽  
Intestinal Fibrosis ◽  
Inflammatory Bowel

Background: Intestinal fibrosis and subsequent strictures represent an important burden in inflammatory bowel disease (IBD). The detection and evaluation of the degree of fibrosis in stricturing Crohn’s disease (CD) is important to address the best therapeutic strategy (medical anti-inflammatory therapy, endoscopic dilation, surgery). Ultrasound elastography (USE) is a non-invasive technique that has been proposed in the field of IBD for evaluating intestinal stiffness as a biomarker of intestinal fibrosis. Objective: The aim of this review is to discuss the ability and current role of ultrasound elastography in the assessment of intestinal fibrosis. Results and Conclusion: Data on USE in IBD are provided by pilot and proof-of-concept studies with small sample size. The first type of USE investigated was strain elastography, while shear wave elastography has been introduced lately. Despite the heterogeneity of the methods of the studies, USE has been proven to be able to assess intestinal fibrosis in patients with stricturing CD. However, before introducing this technique in current practice, further studies with larger sample size and homogeneous parameters, testing reproducibility, and identification of validated cut-off values are needed.

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