Home About us Contact
|
Home About us Contact | ||
|
|
||
Model Checking (model + checking)
Selected AbstractsThe effect of uncontrolled concurrency on model checkingCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 12 2008Donna M. Carter Abstract Correctness of concurrent software is usually checked by techniques such as peer code reviews or code walkthroughs and testing. These techniques, however, are subject to human error, and thus do not achieve an in-depth verification of correctness. Model-checking techniques, which can systematically identify and verify every state that a system can enter, are a powerful alternative method for verifying concurrent systems. However, the usefulness of model checking is limited because the number of states for concurrent models grows exponentially with the number of processes in the system. This is often referred to as the ,state explosion problem.' Some processes are a central part of the software operation and must be included in the model. However, we have found that some exponential complexity results due to uncontrolled concurrency introduced by the programmer rather than due to the intrinsic characteristics of the software being modeled. We have performed tests on multimedia synchronization to show the effect of abstraction as well as uncontrolled concurrency using the Promela/SPIN model checker. We begin with a sequential model not expected to have exponential complexity but that results in exponential complexity. In this paper, we provide alternative designs and explain how uncontrolled concurrency can be removed from the code. Copyright © 2007 John Wiley & Sons, Ltd. [source] Skills Diagnosis Using IRT-Based Latent Class ModelsJOURNAL OF EDUCATIONAL MEASUREMENT, Issue 4 2007Louis A. Roussos This article describes a latent trait approach to skills diagnosis based on a particular variety of latent class models that employ item response functions (IRFs) as in typical item response theory (IRT) models. To enable and encourage comparisons with other approaches, this description is provided in terms of the main components of any psychometric approach: the ability model and the IRF structure; review of research on estimation, model checking, reliability, validity, equating, and scoring; and a brief review of real data applications. In this manner the article demonstrates that this approach to skills diagnosis has built a strong initial foundation of research and resources available to potential users. The outlook for future research and applications is discussed with special emphasis on a call for pilot studies and concomitant increased validity research. [source] Skills Diagnosis Using IRT-Based Continuous Latent Trait ModelsJOURNAL OF EDUCATIONAL MEASUREMENT, Issue 4 2007William Stout This article summarizes the continuous latent trait IRT approach to skills diagnosis as particularized by a representative variety of continuous latent trait models using item response functions (IRFs). First, several basic IRT-based continuous latent trait approaches are presented in some detail. Then a brief summary of estimation, model checking, and assessment scoring aspects are discussed. Finally, the University of California at Berkeley multidimensional Rasch-model-grounded SEPUP middle school science-focused embedded assessment project is briefly described as one significant illustrative application. [source] Residual analysis for spatial point processes (with discussion)JOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES B (STATISTICAL METHODOLOGY), Issue 5 2005A. Baddeley Summary., We define residuals for point process models fitted to spatial point pattern data, and we propose diagnostic plots based on them. The residuals apply to any point process model that has a conditional intensity; the model may exhibit spatial heterogeneity, interpoint interaction and dependence on spatial covariates. Some existing ad hoc methods for model checking (quadrat counts, scan statistic, kernel smoothed intensity and Berman's diagnostic) are recovered as special cases. Diagnostic tools are developed systematically, by using an analogy between our spatial residuals and the usual residuals for (non-spatial) generalized linear models. The conditional intensity , plays the role of the mean response. This makes it possible to adapt existing knowledge about model validation for generalized linear models to the spatial point process context, giving recommendations for diagnostic plots. A plot of smoothed residuals against spatial location, or against a spatial covariate, is effective in diagnosing spatial trend or co-variate effects. Q,Q -plots of the residuals are effective in diagnosing interpoint interaction. [source] Joint Analysis of Time-to-Event and Multiple Binary Indicators of Latent ClassesBIOMETRICS, Issue 1 2004Klaus Larsen Summary. Multiple categorical variables are commonly used in medical and epidemiological research to measure specific aspects of human health and functioning. To analyze such data, models have been developed considering these categorical variables as imperfect indicators of an individual's "true" status of health or functioning. In this article, the latent class regression model is used to model the relationship between covariates, a latent class variable (the unobserved status of health or functioning), and the observed indicators (e.g., variables from a questionnaire). The Cox model is extended to encompass a latent class variable as predictor of time-to-event, while using information about latent class membership available from multiple categorical indicators. The expectation-maximization (EM) algorithm is employed to obtain maximum likelihood estimates, and standard errors are calculated based on the profile likelihood, treating the nonparametric baseline hazard as a nuisance parameter. A sampling-based method for model checking is proposed. It allows for graphical investigation of the assumption of proportional hazards across latent classes. It may also be used for checking other model assumptions, such as no additional effect of the observed indicators given latent class. The usefulness of the model framework and the proposed techniques are illustrated in an analysis of data from the Women's Health and Aging Study concerning the effect of severe mobility disability on time-to-death for elderly women. [source] | ||||||||||