Dynamic graphics for experimental design

When designing an experiment, it is often assumed that the response to be measured can be modelled as a linear function of a vector of parameters plus an error term, y = X[beta] + [epsilon]. Using this model several properties of the design can be defined in terms of the matrix X[superscript]\u27 X, including A-, D-, E- and G-optimality. In this dissertation we review some common design properties and develop new graphical methods for displaying them using dynamic graphics techniques, including interactive updating, linking, animation and rotation. The effects of perturbations to the design on these properties are also displayed, and a new graphical search technique for improving designs is introduced. Our results indicate that these graphs can help to verify the stability of standard experimental designs, highlight weaknesses present in non-standard designs, and suggest possible remedies;In addition, an adaptation of Cook\u27s method for assessing local influence is developed to examine the effects of local perturbations to the model and to the design on selected design properties. Perturbations are made to case weights, design variables, and added variables not included in the assumed model. The design properties examined are D-optimality and the mean squared error of estimating the response at selected points in the design region. Graphical displays are used to interpret the results

Simultaneous quantization of bulk conduction and valence states through adsorption of nonmagnetic impurities on Bi2Se3

Exposing the (111) surface of the topological insulator Bi2Se3 to carbon monoxide results in strong shifts of the features observed in angle-resolved photoemission. The behavior is very similar to an often reported `aging' effect of the surface and it is concluded that this aging is most likely due to the adsorption of rest gas molecules. The spectral changes are also similar to those recently reported in connection with the adsorption of the magnetic adatom Fe. All spectral changes can be explained by a simultaneous confinement of the conduction band and valence band states. This is only possible because of the unusual bulk electronic structure of Bi2Se3. The valence band quantization leads to spectral features which resemble those of a band gap opening at the Dirac point.Comment: 5 pages, 4 figure

Toxaemia of pregnancy and risk of mortality in later life : evidence from the Royal College of General Practitioners' Oral Contraception Study

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Visualizing Experimental Designs for Balanced ANOVA Models using Lisp-Stat

The structure, or Hasse, diagram described by Taylor and Hilton (1981, American Statistician) provides a visual display of the relationships between factors for balanced complete experimental designs. Using the Hasse diagram, rules exist for determining the appropriate linear model, ANOVA table, expected means squares, and F-tests in the case of balanced designs. This procedure has been implemented in Lisp-Stat using a software representation of the experimental design. The user can interact with the Hasse diagram to add, change, or delete factors and see the effect on the proposed analysis. The system has potential uses in teaching and consulting

Wiki or Word? Evaluating Tools for Collaborative Editing and Teamwork

Many college courses involve group work where teams of students are asked to create a report as the final result of a collaborative effort. The creation of such a shared document often causes students great trouble in coordinating the effort. In this paper we describe two approaches to supporting students in collaboratively creating and editing a report for an introductory course in information systems. One group of students used MS Word with Track Changes turned on combined with emailing the document between students. A second group was provided a Twiki site where they were able to create the report. Preliminary analysis shows that students found the Word and email combination more useful and easier to use than the wiki environment in completing the project

Contemporary hormonal contraception and cervical cancer in women of reproductive age

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Contemporary hormonal contraception and risk of endometrial cancer in women younger than age 50 : a retrospective cohort study of Danish women

We thank Drs Lina Mørch and Charlotte Skovlund for their involvement in establishing the collaboration and in the initial discussions about the overall study design whilst they were employed by the University of Copenhagen.Peer reviewedPostprin