# Blog Archives

## Example 9.19: Demonstrating the central limit theorem

January 11, 2012
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A colleague recently asked "why should the average get closer to the mean when we increase the sample size?" We should interpret this question as asking why the standard error of the mean gets smaller as n increases. The central limit theorem shows t...

## Example 9.18: Constructing the fastest relay team via enumeration

January 5, 2012
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In competitive swimming, the medley relay is a team event in which four different swimmers each swim one of the four strokes: freestyle, breaststroke, backstroke, and butterfly. In general, every swimmer might be able swim any given stroke. How can w...

## Example 9.16: Small multiples

November 29, 2011
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Small multiples are one of the great ideas of graphics visionary Edward Tufte (e.g., in Envisioning Information). Briefly, the idea is that if many variations on a theme are presented, differences quickly become apparent. Today we offer general guida...

## Example 9.15: Bar chart with error bars ("Dynamite plot")

November 22, 2011
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The "dynamite plot", a bar chart plotting the a mean with a error bar, is one of the most reviled types of image among statisticians. Reasons to dislike them are numerous, and are nicely summarized here. (Edward Tufte also suggests they be avoided.) ...

## Example 9.13: Negative binomial regression with proc mcmc

November 8, 2011
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In practice, data that derive from counts rarely seem to be fit well by a Poisson model; one more flexible alternative is a negative binomial model. In this SAS-only entry, we discuss how proc mcmc can be used for estimation. An overview of support f...

## Proc report for simple statistics

October 30, 2011
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Ken Beath, of Macquarie University, commented on an earlier entry that the best way to generate summary statistics is using proc report. While the best tools might differ, depending on the purpose, we wanted to share Ken's code demonstrating how to re...

## Example 9.11: Employment plot

October 25, 2011
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A facebook friend posted the picture reproduced above-- it makes the case that President Obama has been a successful creator of jobs, and also paints GW Bush as a president who lost jobs. Another friend pointed out that to be fair, all of Bush's presi...

## Example 9.8: New stuff in SAS 9.3– Bayesian random effects models in Proc MCMC

October 4, 2011
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Rounding off our reports on major new developments in SAS 9.3, today we'll talk about proc mcmc and the random statement.Stand-alone packages for fitting very general Bayesian models using Markov chain Monte Carlo (MCMC) methods have been available for...

## Example 9.7: New stuff in SAS 9.3– Frailty models

September 27, 2011
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Shared frailty models are a way of allowing correlated observations into proportional hazards models. Briefly, instead of l_i(t) = l_0(t)e^(x_iB), we allow l_ij(t) = l_0(t)e^(x_ijB + g_i), where observations j are in clusters i, g_i is typically norma...

## Example 9.6: Model comparison plots (Completed)

September 21, 2011
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We often work in settings where the data set has a lot of missing data-- some missingness in the (many) covariates, some in the main exposure of interest, and still more in the outcome. (Nick describes this as "job security for statisticians").Some ana...

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