# Articles by Jack Davis

### Sampling, conditional probability, and random number generation

October 19, 2021 |

Part of the motivation behind making the course Statistics and Gambling is to infuse new applicability into introductory or intermediate probability courses. This blog post is a look at how the course is going to cover familiar probability topics...

### How does Polychoric Correlation Work? (aka Ordinal-to-Ordinal correlation)

February 14, 2021 |

Let's say you've got data of many paired cases of two ordinal variables, like you might when you ask a large number of people the same two Likert scale questions (e.g. "poor", "fair", "good", "very good", "excellent").   What could you learn from...

### How does Polychoric Correlation Work? (aka Ordinal-to-Ordinal correlation)

February 14, 2021 |

Let's say you've got data of many paired cases of two ordinal variables, like you might when you ask a large number of people the same two Likert scale questions (e.g. "poor", "fair", "good", "very good", "excellent").   What could you learn from...

### R Packette – Fraction Matrix Operations

June 14, 2020 |

Open up any linear algebra textbook and have a look at the matrix entries. Are there all integers? Are they all written as decimals? There's probably at least some that are fractions. Matrices in computer programs are almost always in decimal form. The exception is symbolic mathematics programs like Maple ...

### R Packette – Fraction Matrix Operations

June 14, 2020 |

Open up any linear algebra textbook and have a look at the matrix entries. Are there all integers? Are they all written as decimals? There's probably at least some that are fractions. Matrices in computer programs are almost always in decimal form. T...

### Reversi in R – Part 2: Graphics and Custom Boards

August 8, 2019 |

In this post, I finish the Reversi / Othello game in R by improving the graphics, adding the ability to save and load boards, and fixing bugs. Also, many more boards have been added and tested, including those with unusual shapes, three or more players, and walls that can make the ...

### Reversi in R – Part 1: Bare Bones

July 21, 2019 |

In this post, I showcase a bare-bones point-and-click implementation of the classic board Reversi (also called Othello*) in the R programming language. R is typically used for more serious, statistical endeavors, but it works reasonably well for more playful projects. Building a classic game like this is an excellent high-school ...

### Evaluating Exam Questions using Crowdmark, IRT, and the Generalized Partial Credit Model

November 2, 2017 |

Making good exam questions is universally hard. The ideal question should have a clear solution to those with the requisite understanding, but also difficult enough that someone without the knowledge needed can guess at an answer.An item response theory (IRT) based analysis can estimate the difficulty of a question, ... [Read more...]

### R Seminar on programming with vectors

June 24, 2017 |

This is the first of five seminars that was given at Simon Fraser University. I've included this one in the blog because it makes for, hopefully, an excellent tutorial for intermediate users of R.Inside:- Vector operations- Building a matrix- Matrix operations- Arrays, data frames, and data tables- Indices- ... [Read more...]

### Statistical Thesaurus update, and generating cross-references in R

May 10, 2017 |

The post is about an expansion on the statistics thesaurus that was started in this post. The entries in  The Oxford Dictionary of Statistical Terms, 6th edition, edited by Yadolah Dodge was an inspiration to update the thesaurus, and was used as a 'to do list' of terms to include. ... [Read more...]