Emilio Letón

Inference of the Youden index and associated threshold using empirical likelihood for quantiles

The Youden index is a widely used measure in the framework of medical diagnostics, where the effectiveness of a biomarker (screening marker or predictor) for classifying a disease status is studied. When the biomarker is continuous, it is important to determine the threshold or cut-off point to be used in practice for the discrimination between diseased and healthy populations. We introduce two methods aimed at estimating the Youden index and its associated threshold. The first one is a modified version of a recent approach based on the delta method, and the second one is based on the adjusted empirical likelihood for quantiles in the setting of a two-sample problem. We also include CIs for both of them. In the simulation study, we compare both methods under different scenarios. Finally, a real example of prostatic cancer, well known in the literature, is analysed to provide the reader with a better understanding of the new methodology.

EQUIVALENCE BETWEEN SCORE AND WEIGHTED TESTS FOR SURVIVAL CURVES

In this paper we describe 10 expressions of score and weighted tests, in such a way that the numerators and the denominators are completely specified, including always the possibility of tied observations. We establish the equivalence between score and weighted tests in the general setting of ties. Based upon this equivalence we enunciate two new tests, which complete the jigsaw of the classification of these non-parametric tests in Survival Analysis.

A note on the variances of the tests of kendall, jonckheere, and terpstra

Recently, some papers have been appearing that have noticed some mistakes in the calculations in the statistical software in simple and classical tests (Wilcoxon–Mann-Whitney and Log-Rank). This article examines the variance formulas for the Kendall test, the Jonckheere test, and the Terpstra test. We show in this article that these variances (in spite of what is said in the literature and in the statistical software), in the presence of ties and r ≥ 3 groups, are only equal approximately and are exactly equal for two groups and ties as we prove in the Appendix.

Video podcast and illustrated text feedback in a web-based formative assessment environment

It is well known that computer‐based formative assessment and timely feedback enhance effective student learning but there is still a debate about what type of feedback should be given, being the text‐based the most used feedback in practice. Although the use of video content as a learning resource has recently increased in both educational and non‐educational contexts, there is very little research on its effectiveness as assessment feedback and the existing results are contradictory. For that reason, we have combined in this work the use of a web‐based formative assessment system (Siette) where we have integrated a specific type of video podcast (“modular teaching mini‐videos”: MTMs) and equivalent illustrated text. We have carried out two experiments with a twofold purpose, first to compare the effect of video feedback versus correct response feedback alone and secondly to compare the effect of video feedback versus equivalent illustrated text feedback. In the context of our research, a Statistic Course at university level, our results show, as expected, that there is a statistically significant positive effect in favor of video feedback over correct response feedback alone. Surprisingly, in contrast to our expectations, based on our context of acquisition of procedural knowledge, there is a statistically non‐significant effect of video feedback versus equivalent illustrated text feedback. From the students’ satisfaction survey, there is not statistically significant differences in the overall score of the activity based on video podcast feedback or equivalent illustrated text, which is an indication that we have really obtained equivalent feedback materials.

Confidence intervals for the symmetry point: an optimal cutpoint in continuous diagnostic tests

Continuous diagnostic tests are often used for discriminating between healthy and diseased populations. For this reason, it is useful to select an appropriate discrimination threshold. There are several optimality criteria: the North-West corner, the Youden index, the concordance probability and the symmetry point, among others. In this paper, we focus on the symmetry point that maximizes simultaneously the two types of correct classifications. We construct confidence intervals for this optimal cutpoint and its associated specificity and sensitivity indexes using two approaches: one based on the generalized pivotal quantity and the other on empirical likelihood. We perform a simulation study to check the practical behaviour of both methods and illustrate their use by means of three real biomedical datasets on melanoma, prostate cancer and coronary artery disease.

Two New Concepts in Video Podcasts

Nowadays the main learning resources are traditional board, slides and video podcasts. Each of them with their own strengths and weaknesses. Analysing the advantages and disadvantages of the traditional board and slides we have created, with the advantages of both resources, a new concept that we have named “minimalist slides”. Using the minimalist slides we have introduced a new type of video podcast that we have named “modular teaching mini-video”.