Nonresponse in the Belgian fertility and family survey.

Combining response data from the Belgian Fertility and Family Survey with individual level and municipality level data from the 1991 Census for both nonrespondents and respondents, multilevel logistic regression models for contact and cooperation propensity are estimated. The covariates introduced are a selection of indirect features out of the researcher control only. Contrary to previous research, Socio Economic Status is found to be positively related to cooperation. Another unexpected result is the absence of any considerable impact of ecological correlates such as urbanicity.Cooperation; Data; Design; Fertility and family survey; Logistic regression; Mixture experiment; Model; Models; Multilevel analysis; Nonrespons; Optimal; Optimal design; Process variables; Processes; Qualitative variables; Selection; Split-plot experiment; Variables;

Performance of likelihood-based estimation methods for multilevel binary regression models.

By means of a fractional factorial simulation experiment, we compare the performance of Penalised Quasi-Likelihood, Non-Adaptive Gaussian Quadrature and Adaptive Gaussian Quadrature in estimating parameters for multi-level logistic regression models. The comparison is done in terms of bias, mean squared error, numerical convergence, and computational efficiency. It turns out that, in terms of Mean Squared Error, standard versions of the Quadrature methods perform relatively poor in comparison with Penalized Quasi-Likelihood.Bias; Binary regression; Convergence; Efficiency; Factorial; Fractional factorial experiment; Gaussian quadrature; Logistic regression; Methods; Model; Models; Monte Carlo simulation; Multilevel analysis; Penalised quasi-likelihood; Performance; Regression; Simulation;

Metacognition for spelling in higher etudents with dyslexia: is there evidence for the dual burden hypothesis?

We examined whether academic and professional bachelor students with dyslexia are able to compensate for their spelling deficits with metacognitive experience. Previous research suggested that students with dyslexia may suffer from a dual burden. Not only do they perform worse on spelling but in addition they are not as fully aware of their difficulties as their peers without dyslexia. According to some authors, this is the result of a worse feeling of confidence, which can be considered as a form of metacognition (metacognitive experience). We tried to isolate this metacognitive experience by asking 100 students with dyslexia and 100 matched control students to rate their feeling of confidence in a word spelling task and a proofreading task. Next, we used Signal Detection Analysis to disentangle the effects of proficiency and criterion setting. We found that students with dyslexia showed lower proficiencies but not suboptimal response biases. They were as good at deciding when they could be confident or not as their peers without dyslexia. They just had more cases in which their spelling was wrong. We conclude that the feeling of confidence in our students with dyslexia is as good as in their peers without dyslexia. These findings go against the Dual Burden theory (Kruger & Dunning, 1999), which assumes that people with a skills problem suffer twice as a result of insufficiently developed metacognitive competence. As a result, there is no gain to be expected from extra training of this metacognitive experience in higher education students with dyslexia

Beyond spelling: the writing skills of higher education students with dyslexia

To have a clearer idea of the problems students with dyslexia may face during their studies, we compared writings of 100 students with dyslexia and 100 age matched control students in higher education. The aim of this study was to compare the writing of young adults with dyslexia and young adults without dyslexia. The study was carried out in Belgium with writers of Dutch. First, we studied the number and type of spelling errors, the quality of the texts produced, the use of words, and the handwriting, both in a précis writing task (writing a summary of an informative text) and in a dictation task (sentence writing). Our results showed medium to large effect sizes for spelling errors: d = .93 for morphosyntactic spelling errors, d = .55 for memory-related spelling errors, and a medium effect size for punctuation and capitalization errors, d = .40. Second, experts who were blind to the aims of the study were asked to judge the quality of the writing of both groups based on transcriptions that were free from spelling errors. The quality of the texts produced was judged lower for students with dyslexia than for the controls, d = .61 for text structure and d = .56 for agreeability, even though the number and types of words used by both groups were very much the same. There was no significant difference in the quality of the handwriting, d = .15. Given that remedial teaching has been shown to be effective for essay-writing skills, educational support along these lines may be helpful for students with dyslexia

Deep level transient spectroscopy (DLTS) study of P3HT:PCBM organic solar cells

The electronic structure of an organic photovoltaic bulk heterojunction cell strongly deviates from the typical textbook examples of a single sided junction used to explain electrical characterisation of defects in semiconductors. Therefore it is not so straightforward to assign the capacitance of this device or the charge in it to the presence of a depleted layer within this structure. However, conventional electronic spectroscopic techniques could give useful information to understand the electronic behaviour of the device. Therefore, in this work capacitance and charge DLTS have been performed on P3HT:PCBM solar cells. At 1MHz only negligible variation in the capacitance as a function of temperature and bias has been observed. As a result no spectrum could be recorded using a standard DLTS setup, registering the capacitance at this high frequency. To avoid this parasitic effect low frequency capacitance DLTS (40 kHz) has been performed, showing an anomalous signal with negative amplitude and an activation energy of 160meV, and a complementary positive signal could be observed altering the biases. Charge DLTS clearly revealed that both signals transients, conventional and with altered bias have the same time constants. A recent study has shown that such behaviour cannot be explained by the thermodynamic properties of capture and emission of carriers by a defect in bulk semiconductor. The validity of alternative explanations, including interface states, non-ideal ohmic contacts and effects of carrier hopping on charge mobility, will discussed

Study strategies of first-year undergraduates with and without dyslexia and the effect of gender

For students to be successful in higher education, they need not only have motivation and sufficient intellectual ability, but also a wide range of study skills as well as the metacognitive ability to determine when a change in strategy is needed. We examined whether first-year undergraduates with dyslexia (N = 100) differ from peers without learning disabilities (N = 100) in the use of study strategies. The Learning and Study Strategies Inventory was used and potential gender differences were investigated. Matched for age, gender and field of study, fluid intelligence scores were comparable between groups. The self-reports showed that knowledge of test taking strategies was more limited in the dyslexic group. Also, 'fear of failure' was higher in the dyslexic students. Further analyses revealed group x gender interactions for motivation, time management and fear of failure, with female undergraduates outperforming their male counterparts. Implications for secondary education and university, as well as college student support services are discussed