1,721,103 research outputs found
Model selection via Bayesian information capacity designs for generalised linear models
No full textAbstractThe first investigation is made of designs for screening experiments where the response variable is approximated by a generalised linear model. A Bayesian information capacity criterion is defined for the selection of designs that are robust to the form of the linear predictor. For binomial data and logistic regression, the effectiveness of these designs for screening is assessed through simulation studies using all-subsets regression and model selection via maximum penalised likelihood and a generalised information criterion. For Poisson data and log-linear regression, similar assessments are made using maximum likelihood and the Akaike information criterion for minimally-supported designs that are constructed analytically. The results show that effective screening, that is, high power with moderate type I error rate and false discovery rate, can be achieved through suitable choices for the number of design support points and experiment size. Logistic regression is shown to present a more challenging problem than log-linear regression. Some areas for future work are also indicated
Fractional factorial experiments
No full textFactorial experiments are used to study the effect of simultaneously applying combinations of factors to experimental units. Information on the individual effects of each factor and the way in which the factors interact may be obtained. If only a small number of experimental units is available a fraction of all the possible combinations of factor levels may be used. This results in aliasing of the factorial effects. Useful fractions of factorial experiments have the important factorial effects aliased with effects which are assumed to be negligible. This thesis describes methods of constructing such fractions. Methods of constructing fractions of asymmetrical factorial experiments have been based previously on proportional frequency conditions. Some problems associated with estimating main effects in these fractions are discussed. A family of fractions constructed as the initial block of a single replicate factorial experiment arranged in a generalized cyclic design is studied. These fractions consist of a group of treatment combinations. A general theory is developed including rules for determining the aliasing scheme. The orthogonality of all estimable effects in these fractions is established and a simple method of arranging the fractions in blocks is given. Tables of resolution III and IV fractions are presented. This family of fractions is extended to a wider class of designs formed as the union of cosets of a nontrivial group of treatment combinations. Results are obtained on the aliasing of the main effects of factors in some of these fractions.</p
Continuous optimal designs for generalised linear models under model uncertainty
No full textWe propose a general design selection criterion for experiments where a generalised linear model describes the response. The criterion allows for several competing aims, such as parameter estimation and model discrimination, and also for uncertainty in the functional form of the linear predictor, the link function and the unknown model parameters. A general equivalence theorem is developed for this criterion. In practice, an exact design is required by experimenters and can be obtained by numerical rounding of a continuous design. We derive bounds on the performance of an exact design under this criterion which allow the efficiency of a rounded continuous design to be assessed
All-bias designs for polynomial spline regression models
No full textPolynomial spline regression models of low degree have proved useful in modeling responses from designed experiments in science and engineering when simple polynomial models are inadequate. Where there is uncertainty in the number and location of the knots, or breakpoints, of the spline, then designs that minimize the systematic errors resulting from model misspecification may be appropriate. This paper gives a method for constructing such all-bias designs for a single variable spline when the distinct knots in the assumed and true models come from some specified set. A class of designs is defined in terms of the inter-knot intervals and sufficient conditions are obtained for a design within this class to be all-bias under linear, quadratic and cubic spline models. An example of the construction of all-bias designs is given
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Optimal design for prediction using local linear regression and the DSI-criterion
No full textWhen it is anticipated that data to be collected from an experiment cannot be adequately described by a low-order polynomial, alternative modelling and new design methods are required. Local linear regression, where the response is approximated locally by a series of weighted linear regressions, is an effective nonparametric smoothing method that makes few assumptions about the functional form of the response. We present new methods for the optimal design of experiments for local linear regression, including a new criterion, called DSI-optimality, to find designs that enable precise prediction across a continuous interval. Designs are found numerically for weights defined through the Gaussian and uniform kernels. Theoretical results are presented for the uniform kernel and the special case of prediction at a single point. The sensitivity of the designs to the choice of bandwidth in the local linear regression is studied, and it is found that designs for the Gaussian kernel with large bandwidth have a small number of distinct design points. The methodology is motivated by, and demonstrated on, an experiment from Tribology
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