A Confirmatory Factor Analytic Study Examining the Dimensionality of Educational Achievement Tests

It is important to check the fundamental assumption of most popular Item Response Theory models, unidimensionality. However, it is hard for educational and psychological tests to be strictly unidimensional. The tests studied in this paper are from a standardized high-stake testing program. They feature potential multidimensionality by presenting various item types and item sets. Confirmatory factor analyses with one-factor and bifactor models, and based on both linear structural equation modeling approach and nonlinear IRT approach were conducted. The competing models were compared and the implications of the bifactor model for checking essential unidimensionality were discussed.

Nonlinear tests for genetic studies of complex disease

Linkage and association studies are major analytical tools to search for susceptibility genes for complex diseases. With the availability of large collection of single nucleotide polymorphisms (SNPs) and the rapid progresses for high throughput genotyping technologies, together with the ambitious goals of the International HapMap Project, genetic markers covering the whole genome will be available for genome-wide linkage and association studies. In order not to inflate the type I error rate in performing genome-wide linkage and association studies, multiple adjustment for the significant level for each independent linkage and/or association test is required, and this has led to the suggestion of genome-wide significant cut-off as low as 5 × 10 −7. Almost no linkage and/or association study can meet such a stringent threshold by the standard statistical methods. Developing new statistics with high power is urgently needed to tackle this problem. This dissertation proposes and explores a class of novel test statistics that can be used in both population-based and family-based genetic data by employing a completely new strategy, which uses nonlinear transformation of the sample means to construct test statistics for linkage and association studies. Extensive simulation studies are used to illustrate the properties of the nonlinear test statistics. Power calculations are performed using both analytical and empirical methods. Finally, real data sets are analyzed with the nonlinear test statistics. Results show that the nonlinear test statistics have correct type I error rates, and most of the studied nonlinear test statistics have higher power than the standard chi-square test. This dissertation introduces a new idea to design novel test statistics with high power and might open new ways to mapping susceptibility genes for complex diseases. ^

Bayesian generalized linear models for meta-analysis of diagnostic tests

With the recognition of the importance of evidence-based medicine, there is an emerging need for methods to systematically synthesize available data. Specifically, methods to provide accurate estimates of test characteristics for diagnostic tests are needed to help physicians make better clinical decisions. To provide more flexible approaches for meta-analysis of diagnostic tests, we developed three Bayesian generalized linear models. Two of these models, a bivariate normal and a binomial model, analyzed pairs of sensitivity and specificity values while incorporating the correlation between these two outcome variables. Noninformative independent uniform priors were used for the variance of sensitivity, specificity and correlation. We also applied an inverse Wishart prior to check the sensitivity of the results. The third model was a multinomial model where the test results were modeled as multinomial random variables. All three models can include specific imaging techniques as covariates in order to compare performance. Vague normal priors were assigned to the coefficients of the covariates. The computations were carried out using the 'Bayesian inference using Gibbs sampling' implementation of Markov chain Monte Carlo techniques. We investigated the properties of the three proposed models through extensive simulation studies. We also applied these models to a previously published meta-analysis dataset on cervical cancer as well as to an unpublished melanoma dataset. In general, our findings show that the point estimates of sensitivity and specificity were consistent among Bayesian and frequentist bivariate normal and binomial models. However, in the simulation studies, the estimates of the correlation coefficient from Bayesian bivariate models are not as good as those obtained from frequentist estimation regardless of which prior distribution was used for the covariance matrix. The Bayesian multinomial model consistently underestimated the sensitivity and specificity regardless of the sample size and correlation coefficient. In conclusion, the Bayesian bivariate binomial model provides the most flexible framework for future applications because of its following strengths: (1) it facilitates direct comparison between different tests; (2) it captures the variability in both sensitivity and specificity simultaneously as well as the intercorrelation between the two; and (3) it can be directly applied to sparse data without ad hoc correction. ^

A SIMULATION STUDY OF THE SIZE AND POWER OF SOME TWO-SAMPLE TESTS FOR UNEQUALLY CENSORED SURVIVAL DATA (RANK TESTS, LOGRANK, PROPORTIONAL HAZARDS, WILCOXON TESTS, EXPONENTIAL DISTRIBUTION)

Sizes and power of selected two-sample tests of the equality of survival distributions are compared by simulation for small samples from unequally, randomly-censored exponential distributions. The tests investigated include parametric tests (F, Score, Likelihood, Asymptotic), logrank tests (Mantel, Peto-Peto), and Wilcoxon-Type tests (Gehan, Prentice). Equal sized samples, n = 18, 16, 32 with 1000 (size) and 500 (power) simulation trials, are compared for 16 combinations of the censoring proportions 0%, 20%, 40%, and 60%. For n = 8 and 16, the Asymptotic, Peto-Peto, and Wilcoxon tests perform at nominal 5% size expectations, but the F, Score and Mantel tests exceeded 5% size confidence limits for 1/3 of the censoring combinations. For n = 32, all tests showed proper size, with the Peto-Peto test most conservative in the presence of unequal censoring. Powers of all tests are compared for exponential hazard ratios of 1.4 and 2.0. There is little difference in power characteristics of the tests within the classes of tests considered. The Mantel test showed 90% to 95% power efficiency relative to parametric tests. Wilcoxon-type tests have the lowest relative power but are robust to differential censoring patterns. A modified Peto-Peto test shows power comparable to the Mantel test. For n = 32, a specific Weibull-exponential comparison of crossing survival curves suggests that the relative powers of logrank and Wilcoxon-type tests are dependent on the scale parameter of the Weibull distribution. Wilcoxon-type tests appear more powerful than logrank tests in the case of late-crossing and less powerful for early-crossing survival curves. Guidelines for the appropriate selection of two-sample tests are given. ^

False -positives and false-negatives in tests for trend

False-positive and false-negative values were calculated for five different designs of the trend test and it was demonstrated that a design suggested by Portier and Hoel in 1984 for a different problem produced the lowest false-positive and false-negative rates when applied to historical spontaneous tumor rate data for Fischer Rats. ^

Un cambio de paradigma en la evaluación : De los tests tradicionales a la evaluación de desempeño

Las últimas tendencias en la enseñanza de una lengua extranjera muestran una evolución hacia nuevos enfoques. Sin embargo, las estrategias de evaluación no reflejan en forma fehaciente este cambio de paradigma. Mayoritariamente se continúa priorizando la evaluación formal y sumativa y no se le otorga a la evaluación de proceso la importancia que esta conlleva. El presente trabajo intenta demostrar que la evaluación no puede ser solo concebida como instrumento de medición del aprendizaje del alumno sino que también debe constituir un proceso que proporcione información acerca del camino que el alumno transita en la adquisición de conocimiento, habilidades y actitudes. Es por ello que nos centraremos en la evaluación informal y formativa, haciendo especial hincapié en la evaluación de desempeño, lo que no implica dejar de considerar la evaluación sumativa como parte integral del proceso de enseñanza-aprendizaje. Ejemplos de tareas como evaluación de desempeño pensados para la clase de niños formarán parte de esta propuesta

Un cambio de paradigma en la evaluación : De los tests tradicionales a la evaluación de desempeño

Las últimas tendencias en la enseñanza de una lengua extranjera muestran una evolución hacia nuevos enfoques. Sin embargo, las estrategias de evaluación no reflejan en forma fehaciente este cambio de paradigma. Mayoritariamente se continúa priorizando la evaluación formal y sumativa y no se le otorga a la evaluación de proceso la importancia que esta conlleva. El presente trabajo intenta demostrar que la evaluación no puede ser solo concebida como instrumento de medición del aprendizaje del alumno sino que también debe constituir un proceso que proporcione información acerca del camino que el alumno transita en la adquisición de conocimiento, habilidades y actitudes. Es por ello que nos centraremos en la evaluación informal y formativa, haciendo especial hincapié en la evaluación de desempeño, lo que no implica dejar de considerar la evaluación sumativa como parte integral del proceso de enseñanza-aprendizaje. Ejemplos de tareas como evaluación de desempeño pensados para la clase de niños formarán parte de esta propuesta

Un cambio de paradigma en la evaluación : De los tests tradicionales a la evaluación de desempeño

Las últimas tendencias en la enseñanza de una lengua extranjera muestran una evolución hacia nuevos enfoques. Sin embargo, las estrategias de evaluación no reflejan en forma fehaciente este cambio de paradigma. Mayoritariamente se continúa priorizando la evaluación formal y sumativa y no se le otorga a la evaluación de proceso la importancia que esta conlleva. El presente trabajo intenta demostrar que la evaluación no puede ser solo concebida como instrumento de medición del aprendizaje del alumno sino que también debe constituir un proceso que proporcione información acerca del camino que el alumno transita en la adquisición de conocimiento, habilidades y actitudes. Es por ello que nos centraremos en la evaluación informal y formativa, haciendo especial hincapié en la evaluación de desempeño, lo que no implica dejar de considerar la evaluación sumativa como parte integral del proceso de enseñanza-aprendizaje. Ejemplos de tareas como evaluación de desempeño pensados para la clase de niños formarán parte de esta propuesta

Stable isotope ratios measured on carbonate tests from the Kara Sea

River discharge of Ob and Yenisei to the Kara Sea is highly variable on seasonal and interannual time scales. River water dominates the shallow bottom water near the river mouths, making it warmer and less saline but seasonally and interannually more changeable than bottom water on the deeper shelf. This hydrographic pattern shows up in measurements and modelling, and in stable isotope records (delta18O, delta13C) along the growth axis of bivalve shells and in multiple analyses of single benthic foraminiferal shells. Average isotope ratios increase, but sample-internal variability decreases with water depth and distance from river mouths. However, isotope records of bivalves and foraminifera of a sediment core from a former submarine channel of Yenisei River reveal a different pattern. The retreat of the river mouth from this site due to early Holocene sea level rise led to increasing average isotope values up core, but not to the expected decrease of the in-sample isotope variability. Southward advection of cold saline water along the palaeo-river channel probably obscured the hydrographic variability during the early Holocene. Later, when sediment filled the channel, the hydrographic variability at the core location remained low, because the shallowing proceeded synchronously with the retreat of the river mouth.

A virtual species set for robust and reproducible Species Distribution Modelling tests

Predicting species potential and future distribution has become a relevant tool in biodiversity monitoring and conservation. In this data article we present the suitability map of a virtual species generated based on two bioclimatic variables, and a dataset containing more than 700.000 random observations at the extent of Europe. The dataset includes spatial attributes such as, distance to roads, protected areas, country codes, and the habitat suitability of two spatially clustered species (grassland and forest species) and a wide spread species.