Irene Klugkist

Inequality Constrained Analysis of Variance: A Bayesian approach.

Researchers often have one or more theories or expectations with respect to the outcome of their empirical research. When researchers talk about the expected relations between variables if a certain theory is correct, their statements are often in terms of one or more parameters expected to be larger or smaller than one or more other parameters. Stated otherwise, their statements are often formulated using inequality constraints. In this article, a Bayesian approach to evaluate analysis of variance or analysis of covariance models with inequality constraints on the (adjusted) means is presented. This evaluation contains two issues: estimation of the parameters given the restrictions using the Gibbs sampler and model selection using Bayes factors in the case of competing theories. The article concludes with two illustrations: a one-way analysis of covariance and an analysis of a three-way table of ordered means.

Bayesian evaluation of informative hypotheses

An introduction to bayesian evaluation of informative hypotheses. - Bayesian evaluation of inforative hypotheses. - A further study of prior distributions and the Bayes factor. - Beyond analysis of variance. - Evaluations.

Effectiveness of a Computerised Working Memory Training in Adolescents with Mild to Borderline Intellectual Disabilities

BACKGROUND The goal of this study is to evaluate the effectiveness of a computerised working memory (WM) training on memory, response inhibition, fluid intelligence, scholastic abilities and the recall of stories in adolescents with mild to borderline intellectual disabilities attending special education. METHOD A total of 95 adolescents with mild to borderline intellectual disabilities were randomly assigned to either a training adaptive to each childs progress in WM, a non-adaptive WM training, or to a control group. RESULTS Verbal short-term memory (STM) improved significantly from pre- to post-testing in the group who received the adaptive training compared with the control group. The beneficial effect on verbal STM was maintained at follow-up and other effects became clear at that time as well. Both the adaptive and non-adaptive WM training led to higher scores at follow-up than at post-intervention on visual STM, arithmetic and story recall compared with the control condition. In addition, the non-adaptive training group showed a significant increase in visuo-spatial WM capacity. CONCLUSION The current study provides the first demonstration that WM can be effectively trained in adolescents with mild to borderline intellectual disabilities.

The Bayes factor for inequality and about equality constrained models

The Bayes factor is a useful tool for evaluating sets of inequality and about equality constrained models. In the approach described, the Bayes factor for a constrained model with the encompassing model reduces to the ratio of two proportions, namely the proportion of, respectively, the encompassing prior and posterior in agreement with the constraints. This enables easy and straightforward estimation of the Bayes factor and its Monte Carlo Error. In this set-up, the issue of sensitivity to model specific prior distributions reduces to sensitivity to one prior distribution, that is, the prior for the encompassing model. It is shown that for specific classes of inequality constrained models, the Bayes factors for the constrained with the unconstrained model is virtually independent of the encompassing prior, that is, model selection is virtually objective.

Tactile body image disturbance in anorexia nervosa

Body image disturbances are central to anorexia nervosa (AN). Previous studies have focused mainly on attitudinal and visual aspects. Studies on somatosensory aspects thus far have been scarce. We therefore investigated whether AN patients and controls differed in tactile perception, and how this tactile body image related to visual body image and body dissatisfaction. The Tactile Estimation Task (TET) measured tactile body image: Two tactile stimuli were applied to forearm and abdomen, and, while blindfolded, participants estimated the distance between the two tactile stimuli between their thumb and index finger. The Distance Comparison Task (DCT) measured visual body image. Compared to controls (n=25), AN patients (n=20) not only visualized their body less accurately, but also overestimated distances between tactile stimuli on both the arm and abdomen, which might reflect a disturbance in both visual and tactile body image. High levels of body dissatisfaction were related to more severe inaccuracies in the visual mental image of the body, and overestimation of tactile distances. Our results imply that body image disturbances in AN are more widespread than previously assumed as they not only affect visual mental imagery, but also extend to disturbances in somatosensory aspects of body image.

Bayesian Evaluation of Inequality and Equality Constrained Hypotheses for Contingency Tables

In this article, a Bayesian model selection approach is introduced that can select the best of a set of inequality and equality constrained hypotheses for contingency tables. The hypotheses are presented in terms of cell probabilities allowing researchers to test (in)equality constrained hypotheses in a format that is directly related to the data. The proposed method is investigated by several simulation studies and shows good performance. Software that allows researchers to apply the Bayesian approach to their own data is also provided.

Mental body distance comparison: a tool for assessing clinical disturbances in visual body image.

Despite numerous body size estimation studies, it cannot be concluded that the disturbance of body image in anorexia nervosa (AN) is specifically one of the visual body images. We adopted a visual imagery method, the Distance Comparison task, to enable across-population testing of differences in visual body image with respect to shape. Participants were asked to mentally scan across two body widths (e.g. hips and shoulders) and to decide as quickly as possible which one was longer or shorter. If the mental representation accessed to make such comparisons is visual, an inverse relation would be expected between RT and distance difference on the body to be judged (i.e. actual difference in size between the two body widths), with accuracy increasing with increasing distance difference. Females with high body shape concern (scoring high on the Body Shape Questionnaire: BSQ, n=23) were compared to females with low body shape concern (scoring low on the BSQ, n=19). RT and distance differences on the body demonstrated standard distance differences effects: RT increased and accuracy decreased with decreasing distance differences on the body. Groups differed with respect to accuracy, in that females high on body shape concern were significantly less accurate than females low on body shape concern when making evaluations involving small (9cm) differences, which implies a less appropriate visual image of the own body in the former group. With respect to the relation between RT and body distance difference, on the other hand, there were no differences between groups. We concluded that evaluations of own body size employ visual imagery and that the distance comparison task holds promise for the assessment of visual disturbances in body image in clinical populations.

Do we know what we test and do we test what we want to know

Null hypothesis testing (NHT) is the most commonly used tool in empirical psychological research even though it has several known limitations. It is argued that since the hypotheses evaluated with NHT do not reflect the research-question or theory of the researchers, conclusions from NHT must be formulated with great modesty, that is, they cannot be stated in a confirmative way. Since confirmation or theory evaluation is, however, what researchers often aim for, we present an alternative approach that is based on the specification of explicit, informative statistical hypotheses. The statistical approach for the evaluation of these hypotheses is a Bayesian model-selection procedure. A non-technical explanation of the Bayesian approach is provided and it will be shown that results obtained with this method give more direct answers to the questions asked and are easier to interpret. An additional advantage of the offered possibility to formulate and evaluate informative hypotheses is that it stimulates researchers to more carefully think through and specify their expectations.

Incorporation of historical data in the analysis of randomized therapeutic trials

Historical studies provide a valuable source of information for the motivation and design of later trials. Bayesian techniques offer possibilities for the quantitative inclusion of prior knowledge within the analysis of current trial data. Combining information from previous studies into an informative prior distribution is, however, a delicate case. The power prior distribution is a tool to estimate the effect of an intervention in a current study sample, while accounting for the information provided by previous research. In this study we evaluate the use of the power prior distribution, illustrated with data from a large randomized clinical trial on the effect of ST-wave analysis in intrapartum fetal monitoring. We advocate the use of a power prior distribution with pre-specified fixed study weights based on differences in study characteristics. We propose obtaining a ranking of the historical studies via expert elicitation, based on relevance for the current study, and specify study weights accordingly.

Cognitive behavioral variables mediate the associations of neuroticism and attachment insecurity with Prolonged Grief Disorder severity

Abstract Prolonged Grief Disorder (PGD) is a debilitating syndrome of grief. A recent cognitive behavioral model asserts that three processes are critical to this condition: (1) insufficient integration of the loss with autobiographical knowledge about the self and the lost person; (2) negative cognitions; and (3) anxious and depressive avoidance behaviors. These processes are assumed to contribute to PGD symptoms and to mediate the influence of personality-related vulnerabilities on the development and maintenance of these symptoms. The present study examined the mediational role of these three processes in the linkage between neuroticism, attachment anxiety, and attachment avoidance on the one hand and PGD symptom severity on the other hand. Self-reported data from 348 bereaved people were used. The results showed that the three personality variables were significantly associated with PGD symptom severity. Moreover, the results provided support for the mediating effects of indices of insufficient integration, negative cognitions, as well as avoidance behaviors – even after controlling for the shared variance between mediators. Theoretical and clinical implications are discussed.