# Articles by

### S is for semPlot Package

April 21, 2018 |

S is for semPlotToday's post is on my favorite, "where have you been all my statistical life?" package, semPlot. When I took my first structural equation modeling course 11 years ago, for our final project, we had to use one of the models we learned in the course on a set ...

### R is for R Origin Story

April 20, 2018 |

An important place in the history of statistics is AT&T Bell Laboratories. And one of the key parts of that story is the development of a language for statistical computing called S.Prior to 1975 or so, statistical researchers at Bell Labs used For...

### Q is for qplot

April 19, 2018 |

Q is for qplotYou may have noticed that I frequently use the ggplot2 package and the ggplot function to produce graphics for my posts. ggplot2, which is part of the so-called tidyverse, is called gg to refer to the "grammar of graphics". That is, it uses standard functions and arguments ...

### P is for Principal Components Analysis (PCA)

April 18, 2018 |

P is for Principal Components Analysis This month, I've talked about some approaches for testing the underlying latent variables (or factors) in a set of measurement data. Confirmatory factor analysis is one method of examining latent variables when you know ahead of time which observed variables are associated with which ... [Read more...]

### O is for Overview Reports

April 17, 2018 |

O is for overview Reports with dataMaidOne of the best things you can do is to create a study codebook to accompany your dataset. In it, you should include information about the study variables and how they were created/computed. It's also nice to have a summary of your dataset, ... [Read more...]

### N is for N (Sample Size) Estimation: Power Analysis in R

April 16, 2018 |

N Estimation We're pushing forward in the Blogging A to Z Challenge! Today, I'll talk about conducting power analyses in R with the pwr package. It's amazing the number of studies designed and conducted without the aid of power analysis. Once I learned how to do them in grad school, ...

### Statistics Sunday: Fit Statistics in Structural Equation Modeling

April 15, 2018 |

Fit Measures In my video on interpreting confirmatory factor analysis output, I promised a post on the various fit statistics. And here we are! As I said in the video, when you conduct structural equation modeling, the program is comparing the observed data - specifically the observed covariance matrix - ... [Read more...]

### M is for R Markdown Files

April 14, 2018 |

Today's A to Z of R will be a bit different from previous ones in that the focus is not on how to code something in R, but how to use a feature in R Studio to create documents, such as HTML and PDF. Either of these types of documents ...

### L is for Latent Variable Path Analysis

April 13, 2018 |

LVPAFor the letter F, I introduced the lavaan package with confirmatory factor analysis. You may have noticed, during my video on interpreting output that there are two functions for analysis: cfa and sem. When the model you specify is a confirmatory factor analysis, it doesn't really matter which of these ...

### K is for Cohen’s Kappa

April 12, 2018 |

Last April, during the A to Z of Statistics, I blogged about Cohen's kappa, a measure of interrater reliability. Cohen's kappa is a way to assess whether two raters or judges are rating something the same way. And thanks to an R package called irr, it's very easy to compute. ...

### J is for jsonlite Package

April 11, 2018 |

J is for jsonlite packageToday I'm going to introduce a new method of storing and exchanging data: JSON or JavaScript Object Notation. Up to now, we've been working with delimited text files and R data frames. But JSON (pronounced "Jason") is another way we can store data that can be ...

### I is for (Classical) Item Analysis or I Must Be Flexible

April 10, 2018 |

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...]

### H is for Help with R

April 9, 2018 |

My goal this month is to offer some fun tutorials and introductions to the R statistical language and R Studio software. But you may find, at some point, that you need a little...And that's okay! R can have a very steep learning curve, but even for an ...

### Statistics Sunday: Interpreting Confirmatory Factor Analysis Output

April 8, 2018 |

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...]

### G is for GLM Function

April 7, 2018 |

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...]

### Hillslope Position by Soil Series

June 5, 2013 |

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...]

February 9, 2013 |

### Automated OSD Lookup and Display via SoilWeb and AQP

November 8, 2012 |

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...]

### Combining Base+Grid Graphics

October 4, 2012 |

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...]

### AQP Demo: Applying a Function to Each Soil Profile in a Collection with profileApply()

June 19, 2012 |

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...]
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