Blog Archives

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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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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Veterinary Epidemiologic Research: Linear Regression

February 14, 2013
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Veterinary Epidemiologic Research: Linear Regression

This post will describe linear regression as from the book Veterinary Epidemiologic Research, describing the examples provided with R. Regression analysis is used for modeling the relationship between a single variable Y (the outcome, or dependent variable) measured on a continuous or near-continuous scale and one or more predictor (independent or explanatory variable), X. If

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Reproducible Research Using Sweave and LaTeX

June 8, 2012
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Reproducible Research Using Sweave and LaTeX

Here are the slides given during the Montreal R User Group workshop on April 30, 2012. RR-MtlRUsers.beamer

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Beeswarm Plot with ggplot2

September 16, 2011
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Beeswarm Plot with ggplot2

A colleague showed me results of his study project with beeswarm plots made by GraphPad. I was wondering if it could be implemented in R and more specifically with ggplot2. There is a R package allowing to draw such graphs, the beeswarm package (beeswa...

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R, JAGS and ggplot2

May 24, 2011
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R, JAGS and ggplot2

Last week a question was asked on the ggplot2 list about using ggplot2 and jags in R (). Here’s what was my answer (a bit updated): Using as an example the school dataset from R2WinBUGS package: Than you can use the mcmcplots package which give a “feel” of ggplot2: If you really want to use

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Publishing in Veterinary Academic Journals

May 10, 2011
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Publishing in Veterinary Academic Journals

Following the post by Arthur Charpentier (Freakonometrics), I wondered what would be the outcome considering my current engagement (veterinary medicine, epidemiology, bovine mastitis). Briefly, Arthur Charpentier’s post looked at clusters of journals publishing the same kind of papers. So I looked at 25 journals (Journal of Dairy Science, Canadian Journal of Veterinary Medicine, Preventive Veterinary

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