1145 search results for "latex"

Simulating Random Multivariate Correlated Data (Categorical Variables)

March 11, 2013
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Simulating Random Multivariate Correlated Data (Categorical Variables)

This is a repost of the second part of an example that I posted last year but at the time I only had the PDF document (written in ). This is the second example to generate multivariate random associated data. This example shows how to generate ordinal, categorical, data. It is a little more complex than generating continuous

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Veterinary Epidemiologic Research: Linear Regression Part 3 – Box-Cox and Matrix Representation

March 11, 2013
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Veterinary Epidemiologic Research: Linear Regression Part 3 – Box-Cox and Matrix Representation

In the previous post, I forgot to show an example of Box-Cox transformation when there’s a lack of normality. The Box-Cox procedure computes values of which best “normalises” the errors. value Transformed value of Y 2 1 0.5 0 -0.5 -1 -2 For example: The plot indicates a log transformation. Matrix Representation We can use

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Simulating Random Multivariate Correlated Data (Continuous Variables)

March 11, 2013
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Simulating Random Multivariate Correlated Data (Continuous Variables)

This is a repost of an example that I posted last year but at the time I only had the PDF document (written in ).  I’m reposting it directly into WordPress and I’m including the graphs. From time-to-time a researcher needs to develop a script or an application to collect and analyze data. They may also need

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Analyse Quandl data with R – even from the cloud

March 10, 2013
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Analyse Quandl data with R – even from the cloud

I have read two thrilling news about the really promising time-series data provider called Quandl recently: Quandl: A Wikipedia for Time Series DataQuandl package released to CRANWith the help of the Quandl R package* (development version...

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Comparing quantiles for two samples

March 8, 2013
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Comparing quantiles for two samples

Recently, for a research paper, I some samples, and I wanted to compare them. Not to compare they means (by construction, all of them were centered) but there dispersion. And not they variance, but more their quantiles. Consider the following boxplot type function, where everything here is quantile related (which is not the case for standard boxplot, see http://freakonometrics.hypotheses.org/4138,...

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Veterinary Epidemiologic Research: Linear Regression Part 2 – Checking assumptions

March 6, 2013
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Veterinary Epidemiologic Research: Linear Regression Part 2 – Checking assumptions

We continue on the linear regression chapter the book Veterinary Epidemiologic Research. Using same data as last post and running example 14.12: Now we can create some plots to assess the major assumptions of linear regression. First, let’s have a look at homoscedasticity, or constant variance of residuals. You can run a statistical test, the

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Stan 1.2.0 and RStan 1.2.0

March 6, 2013
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Stan 1.2.0 and RStan 1.2.0

Stan 1.2.0 and RStan 1.2.0 are now available for download. See: http://mc-stan.org/ Here are the highlights. Full Mass Matrix Estimation during Warmup Yuanjun Gao, a first-year grad student here at Columbia (!), built a regularized mass-matrix estimator. This helps for posteriors with high correlation among parameters and varying scales. We’re still testing this ourselves, so The post Stan...

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Barycentric interpolation: fast interpolation on arbitrary grids

March 6, 2013
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Barycentric interpolation: fast interpolation on arbitrary grids

Barycentric interpolation generalises linear interpolation to arbitrary dimensions. It is very fast although suboptimal if the function is smooth. You might now it as algorithm 21.7.1 in Numerical Recipes (Two-dimensional Interpolation on an Irregular Grid). Using package geometry it can be implemented in a few lines of code in R. Here’s a quick explanation of what

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Tools for making a paper

March 1, 2013
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Since it seems to be the fashion, here’s a post about how I make my academic papers. Actually, who am I trying to kid? This is also about how I make slides, letters, memos and “Back in 10 minutes” signs to pin on the door. Nevertheless it’s for making academic papers that I’m going to

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How to make a scientific result disappear

February 27, 2013
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How to make a scientific result disappear

Nathan Danneman (a co-author and one of my graduate students from Emory) recently sent me a New Yorker article from 2010 about the “decline effect,” the tendency for initially promising scientific results to get smaller upon replication. Wikipedia can summarize the phenomenon as well as I can: In his article, Lehrer gives several examples where

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