Blog Archives

Using the "Divide by 4 Rule" to Interpret Logistic Regression Coefficients

December 6, 2010
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I was recently reading a bit about logistic regression in a book on hierarchical/multilevel modeling when I first learned about the "divide by 4 rule" for quickly interpreting coefficients in a logistic regression model in terms of the predicted probabilities of the outcome. The idea is pretty simple. The logistic curve (predicted probabilities) is steepest at the center where...

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Syntax Highlighting R Code, Revisited

November 17, 2010
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A few months ago I showed you how to syntax-highlight R code using Github Gists for displaying R code on your blog or other online medium. The idea's really simple if you use blogger - head over to gist.github.com, paste in your R code, create a public "gist", hit "embed", then copy the javascript onto your blog. However, if...

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Install and load R package "Rcmdr" to quickly install lots of other packages

September 21, 2010
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I recently reformatted my laptop and needed to reinstall R and all the packages that I regularly use. In a previous post I covered R Commander, a nice GUI for R that includes a decent data editor and menus for graphics and basic statistical analysis. Since Rcmdr depends on many other packages, installing and loading Rcmdr like this...install.packages("Rcmdr", dependencies=TRUE)library(Rcmdr) ..

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Embed R Code with Syntax Highlighting on your Blog

September 7, 2010
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If you use blogger or even wordpress you've probably found that it's complicated to post code snippets with spacing preserved and syntax highlighting (especially for R code). I've discovered a few workarounds that involve hacking the blogger HTML templ...

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Writing my Thesis – Follow me on Twitter

August 31, 2010
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A few weeks ago I suddenly reached the point that every graduate student once thought would never come - time to start writing my thesis. With a blank page and a blinking cursor staring me in the face it's time to compile all of my published and unpubl...

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Deducer: R and ggplot2 GUI

August 16, 2010
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Last Year I introduced you to R Commander, a nice graphical user interface (GUI) for R for those of you who are still hesitant to leave the clicky-box style research a la SPSS for the far more superior reproducible research using R. As most of you know...

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Quickly Find the Class of data.frame vectors in R

August 9, 2010
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Aviad Klein over at My ContRibution wrote a convenient R function to list the classes of all the vectors that make up a data.frame. You would think apply(kyphosis,2,class) would do the job but it doesn't - it calls every vector a character class. Aviad wrote an elegant little function that does the job perfectly without having to load any...

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Hadley Wickham’s ggplot2 / Data Visualization Course Materials

July 27, 2010
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Hadley Wickham, creator of ggplot2, an immensely popular framework for Tufte-friendly data visualization using R, is teaching two short courses at Vanderbilt this week. Once we opened registration to Vanderbilt students and staff we instantly filled al...

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QQ plot of p-values in R using base graphics

July 14, 2010
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Update Tuesday, September 14, 2010: Fixed the ylim issue, now it sets the y axis limit based on the smallest observed p-value.A while back Will showed you how to create QQ plots of p-values in Stata and in R using the now-deprecated sma package. A bi...

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All code on GGD is Free (Open Source BSD)

July 7, 2010
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At the request of a commenter I just wanted to clarify that any code released here for R or anything else is free and open source unless specifically stated otherwise. The open source BSD license for any code on GGD can be found on this copyright page.

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