# Statistics

## September Talks

To celebrate my last full month on the East Coast, I’m doing a bunch of talks. If you’re interested in hearing more about Julia or statistics in general, you might want to come out to one of the events I’ll be at: Julia Tutorial at DataGotham: On 9/12, Stefan and I will be giving a […]

## Hopfield Networks in Julia

As a fun side project last night, I decided to implement a basic package for working with Hopfield networks in Julia. Since I suspect many of the readers of this blog have never seen a Hopfield net before, let me explain what they are and what they can be used for. The short-and-skinny is that […]

## What’s Next

The last two weeks have been full of changes for me. For those who’ve been asking about what’s next, I thought I’d write up a quick summary of all the news. (1) I successfully defended my thesis this past Monday. Completing a Ph.D. has been a massive undertaking for the past five years, and it’s […]

## Using Norms to Understand Linear Regression

Introduction In my last post, I described how we can derive modes, medians and means as three natural solutions to the problem of summarizing a list of numbers, $$(x_1, x_2, \ldots, x_n)$$, using a single number, $$s$$. In particular, we measured the quality of different potential summaries in three different ways, which led us to […]

## Modes, Medians and Means: A Unifying Perspective

Introduction / Warning Any traditional introductory statistics course will teach students the definitions of modes, medians and means. But, because introductory courses can’t assume that students have much mathematical maturity, the close relationship between these three summary statistics can’t be made clear. This post tries to remedy that situation by making it clear that all […]

## Writing Better Statistical Programs in R

A while back a friend asked me for advice about speeding up some R code that they’d written. Because they were running an extensive Monte Carlo simulation of a model they’d been developing, the poor performance of their code had become an impediment to their work. After I looked through their code, it was clear […]

## Americans Live Longer and Work Less

Today I saw an article on Hacker News entitled, “America’s CEOs Want You to Work Until You’re 70″. I was particularly surprised by this article appearing out of the blue because I take it for granted that America will eventually have to raise the retirement age to avoid bankruptcy. After reading the article, I wasn’t […]

## Symbolic Differentiation in Julia

A Brief Introduction to Metaprogramming in Julia In contrast to my previous post, which described one way in which Julia allows (and expects) the programmer to write code that directly employs the atomic operations offered by computers, this post is meant to introduce newcomers to some of Julia’s higher level functions for metaprogramming. To make […]

## Computers are Machines

When people try out Julia for the first time, many of them are worried by the following example: 1 2 3 4 5 6 7 julia> factorial(n) = n == 0 ? 1 : n * factorial(n – 1)   julia> factorial(20) 2432902008176640000   julia> factorial(21) -4249290049419214848 If you’re not familiar with computer architecture, this […]

## What is Correctness for Statistical Software?

Introduction A few months ago, Drew Conway and I gave a webcast that tried to teach people about the basic principles behind linear and logistic regression. To illustrate logistic regression, we worked through a series of progressively more complex spam detection problems. The simplest data set we used was the following: This data set has […]