Blog Archives

R resources

December 3, 2014
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This is the third in my weekly series of posts pointing out resources on this site. This week’s topic is R. R language for programmers Default arguments and lazy evaluation in R Distributions in R Moving data between R and Excel via the clipboard Sweave: First steps toward reproducible analyses Troubleshooting Sweave Regular expressions in […]

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Random probability tweets

December 3, 2014
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For the next few weeks, I’ve scheduled @ProbFact tweets to come out at random times. They will follow a Poisson distribution with an average of two per day. (Times are truncated to multiples of 5 minutes because my scheduling software requires that.)  

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First two impressions of statistics

November 25, 2014
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When I was a postoc I asked a statistician a few questions and he gave me an overview of his subject. (My area was PDEs; I knew nothing about statistics.) I remember two things that he said. A big part of being a statistician is knowing what to do when your assumptions aren’t met, because […]

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Blue Bonnet Bayes

October 28, 2014
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Blue Bonnet Bayes

Blue Bonnet™ used to run commercials with the jingle “Everything’s better with Blue Bonnet on it.” Maybe they still do. Perhaps in reaction to knee-jerk antipathy toward Bayesian methods, some statisticians have adopted knee-jerk enthusiasm for Bayesian methods. Everything’s better with Bayesian analysis on it. Bayes makes it better, like a little dab of margarine […]

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How well does sample range estimate range?

October 25, 2014
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How well does sample range estimate range?

I’ve been doing some work with Focused Objective lately, and today the following question came up in our discussion. If you’re sampling from a uniform distribution, how many samples do you need before your sample range has an even chance of covering 90% of the population range? This is a variation on a problem I’ve […]

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Common sense and statistics

September 18, 2014
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College courses often begin by trying to weaken your confidence in common sense. For example, a psychology course might start by presenting optical illusions to show that there are limits to your ability to perceive the world accurately. I’ve seen at least one physics textbook that also starts with optical illusions to emphasize the need […]

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Intuition and Data at KeenCON

August 14, 2014
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Intuition and Data at KeenCON

I will be giving a talk “Bayesian statistics as a way to integrate intuition and data” at KeenCon, September 11, 2014 in San Francisco. Update: Use promo code KeenCon-JohnCook to get 75% off registration.

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Chances of being picked twice for drug testing

June 18, 2014
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Chances of being picked twice for drug testing

Suppose in a company of N employees, m are chosen randomly for drug screening [1]. In two independent screenings, what is the probability that someone will be picked both times? It may be unlikely that any given individual will be picked twice, while being very likely that someone will be picked twice. Imagine m employees […]

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Normal approximation details

May 29, 2014
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The normal distribution can approximate many other distributions, though the details such as quantitative error estimates and what factors improve or degrade the approximation are harder to find. Here are some notes on normal approximations to several ...

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Robust in one sense, sensitive in another

May 14, 2014
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When you sort data and look at which sample falls in a particular position, that’s called order statistics. For example, you might want to know the smallest, largest, or middle value. Order statistics are robust in a sense. The median of a sample, for example, is a very robust measure of central tendency. If Bill […]

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