I wanted to thank those of you who have emailed and commented on my last post and its Link to Item Response Theory Presentations Using R. In the Psychometrics Centre website, it is not until Topic 7 called Unidimensional IRT models for binar...

I wanted to thank those of you who have emailed and commented on my last post and its Link to Item Response Theory Presentations Using R. In the Psychometrics Centre website, it is not until Topic 7 called Unidimensional IRT models for binar...

IntroductionSo a little while ago I quit my job.Well, actually, that sounds really negative. I'm told that when you are discussing large changes in your life, like finding a new career, relationship, or brand of diet soda, it's important to frame things positively.So let me rephrase that - I've left job I previously held to pursue other directions. Why?...

The other night in my office I got into a discussion with my office mate, the brilliant scientist / amazing skier Dr. Thor Veen about how to understand the random effect variance term in a mixed-effects model. Thor teaches the R statistics course here at UBC, and last night a student came to the office...

What are trees? Trees (also called decision trees, recursive partitioning) are a simple yet powerful tool in predictive statistics. The idea is to split the covariable space into many partitions and to fit a constant model of the response variable in each partition. In case of regression, the mean...

Today at Davis R Users’ Group, Rosemary Hartman took us through her work in progress fitting general additive models to organism presence/absence data. Below is her presentation and script. You can get the original script and data here Also, check the comments below for some discussion of other options for this type of analysis, such as...

I recently had a task to take a look at some assessment (audit) data. I was assuming, rather hoping for data with a normal distribution and thought it would be a quick case of Pearson correlation between two columns: "Duration" and "Score". Just conjecture at this point as I did not understand what the assessment process

As promised, the source distribution for R 2.15.2 is now available for download from the master CRAN repository. (Binary distributions for Windows, MacOS and Linux will be available from the CRAN mirror network in the coming days.) This latest point-update — codenamed "Trick or Treat" — improves the performance of the R engine and adds a few minor but...

I was creating a dataset this last week in which I had to partition the observed responses to show how the ANOVA model partitions the variability. I had the observed Y (in this case prices for 113 bottles of wine), … Continue reading →