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- Athanasios Kottas, Márcia D. Branco, Alan E. Gelfand
- Biometrics
- 2002

In cytogenetic dosimetry, samples of cell cultures are exposed to a range of doses of a given agent. In each sample at each dose level, some measure of cell disability is recorded. The objective is to develop models that explain cell response to dose. Such models can be used to predict response at unobserved doses. More important, such models can provide… (More)

- Pulak Ghosh, Márcia D. Branco, Hrishikesh Chakraborty
- Statistics in medicine
- 2007

Correlated data arise in a longitudinal studies from epidemiological and clinical research. Random effects models are commonly used to model correlated data. Mostly in the longitudinal data setting we assume that the random effects and within subject errors are normally distributed. However, the normality assumption may not always give robust results,… (More)

We introduce a new skew-probit link for item response theory (IRT) by considering an accumulated skew-normal distribution. The model extends the symmetric probit-normal IRT model by considering a new item (or skewness) parameter for the item characteristic curve. A special interpretation is given for this parameter, and a latent linear structure is… (More)

In this work we approach the problem of model comparison between skew families. For the univariate skew model, we measure the sensitivity of the skewness parameter using the L1-distance between symmetric and asymmetric models and we obtain explicit expressions for some of these models. The main result is that the L1-distance between a representable… (More)

- Rolando De la Cruz, Márcia D. Branco
- Biometrical journal. Biometrische Zeitschrift
- 2009

We have considered a Bayesian approach for the nonlinear regression model by replacing the normal distribution on the error term by some skewed distributions, which account for both skewness and heavy tails or skewness alone. The type of data considered in this paper concerns repeated measurements taken in time on a set of individuals. Such multiple… (More)

We introduce a generalized skew probit (gsp) class of links for the modeling of binary regression giving some properties and conditions for the existence of the maximum likelihood estimator and of the posterior distributions of the parameters of the model when improper uniform priors are established. As shown, asymmetric links already proposed in the… (More)

We study the Jeffreys prior and its properties for the shape parameter of univariate skew-t distributions with linear and nonlinear Student’s t skewing functions. In both cases, we show that the resulting priors for the shape parameter are symmetric around zero and proper. Moreover, we propose a Student’s t approximation of the Jeffreys prior that makes an… (More)

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