I is for ITEMAN Back when I worked at HMH, I discovered an R package called ITEMAN, which is used for classical item analysis. I've mentioned classical test theory before, which focuses on the overall test or measure, as opposed to individual items. Tests and measures developed with classical test ... [Read more...]

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It's a Deeply Trivial first - I made my first video! In it, I talk through conducting and interpreting the output of the analyses from the F is for (Confirmatory) Factor Analysis post.Also referenced in the video:Goodness of Fit post - a reminder of ho... [Read more...]

In the Beta post, I used linear regression and demonstrated how to request standardized regression coefficients (betas). You may remember that I mentioned in that post that there are other types of regression. Linear regression is used with a continouous outcome. But sometimes you want to predict outcomes that aren't ... [Read more...]

Soil survey data are typically built upon a foundation of soil-landscape relationships that have been verified in the field. SSURGO data contain several geomorphic descriptions of landscape, landform, hillslope position, and surface shape for each... [Read more...]

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UPDATED 2013-04-08 This functionality it now available in the soilDB and sharpshootR packages. All code on this page is now superseded by the fetchOSD() and SoilTaxonomyDendrogram()functions. UPDATED 2012-11-07 I have been thinking about a URL-ba... [Read more...]

R provides several frameworks for composing figures. Base graphics is the simplest, grid is more advanced, and the lattice/ggplot packages provide convenient abstractions of the grid graphics system. Multi-element figures can be readily created in... [Read more...]

Here is a quick demonstration of how functionality from the AQP package can be used to answer complex soils-related questions. In these examples the profileApply() function is used to iterate over a collection of soil profiles, and compute severa... [Read more...]