# Blog Archives

## Divide by 4 Rule for Marginal Effects

May 25, 2016
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Previously I wrote about the practical differences between marginal effects and odds ratios with regard to logistic regression. Recently, I ran across a tweet from Michael Grogan linking to one of his posts using logistic regression to model dividend probabilities. This really got me interested:"Moreover, to obtain a measure in probability terms – one could divide the...

## SAS vs R? The right answer to the wrong question?

June 13, 2015
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For a long time I tracked a discussion on LinkedIn that consisted of various opinions about using SAS vs R. Some people can take this very personal.  Recently there was an interesting post at the DataCamp blog addressing this topic. They also prov...

## Using the R MatchIt package for propensity score analysis

March 28, 2015
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Descriptive analysis between treatment and control groups can reveal interesting patterns or relationships, but we cannot always take descriptive statistics at face value. Regression and matching methods allow us to make controlled comparisons to reduc...

June 19, 2013
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## Why does IFELSE logic work differently on what appear to be the same values?

February 22, 2013
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Embarrassingly I'm stumped on this...I have a program in R for looking at grade distributions in my class. I found something weird recently with my 'ifelse' processing. I noticed that my program seemed to be over counting Cs and under counting...

## Decomposition: The Statistics Software Signal

January 8, 2013
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From: Decomposition: The Statistics Software Signal http://seanjtaylor.com/post/39573264781/the-statistics-software-signal"When you don't have to code your own estimators, you probably won't understand what you're doing. I'm not saying that you defini...

## Data science = failure of imagination

January 8, 2013
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From: http://www.r-bloggers.com/data-driven-science-is-a-failure-of-imagination/I think I like this distinction between Bayesian and Frequentist statistics: "we are nearly always ultimately curious about the Bayesian probability of the hypothesis ...

## How John Deere uses R

November 10, 2012
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HT: Revolution Analytics  Very good discussion about real applied econometrics and analytics including the use of ARIMA models, decision trees, and genetic algorithms. He also has a very smart approach in his attitude toward big data and data s...

## R Code for A Justification and Application of Eigenvector Centrality

November 8, 2012
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Leo Spizzirri  does an excellent job of providing mathematical intuition behind eigenvector centrality. As I was reading through it, I found it easier to just work through the matrix operations he proposes using R.  You can find his paper her...

## Nonnegative Matrix Factorization and Recommendor Systems

October 24, 2012
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Albert Au Yeung provides a very nice tutorial on non-negative matrix factorization and an implementation in python. This is based very loosely on his approach. Suppose we have the following matrix of users and ratings on movies:If we use the information above to form a matrix R it can be decomposed into two matrices...