Posts Tagged ‘ data analysis ’

Visualize a design matrix

April 26, 2017
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Visualize a design matrix

Most SAS regression procedures support a CLASS statement which internally generates dummy variables for categorical variables. I have previously described what dummy variables are and how are they used. I have also written about how to create design matrices that contain dummy variables in SAS, and in particular how to

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Visualize an ANOVA with two-way interactions

April 24, 2017
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Visualize an ANOVA with two-way interactions

There are several ways to visualize data in a two-way ANOVA model. Most visualizations show a statistical summary of the response variable for each category. However, for small data sets, it can be useful to overlay the raw data. This article shows a simple trick that you can use to

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Regression with restricted cubic splines in SAS

April 19, 2017
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Regression with restricted cubic splines in SAS

Restricted cubic splines are a powerful technique for modeling nonlinear relationships by using linear regression models. I have attended multiple SAS Global Forum presentations that show how to use restricted cubic splines in SAS regression procedures. However, the presenters have all used the %RCSPLINE macro (Frank Harrell, 1988) to generate

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Find your birthday in the digits of pi

March 13, 2017
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Find your birthday in the digits of pi

It is time for Pi Day, 2017! Every year on March 14th (written 3/14 in the US), geeky mathematicians and their friends celebrate "all things pi-related" because 3.14 is the three-decimal approximation to pi. This year I use SAS software to show an amazing fact: you can find your birthday

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Quantile estimates and the difference of medians in SAS

February 22, 2017
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Quantile estimates and the difference of medians in SAS

Sometimes SAS programmers ask about how to analyze quantiles with SAS. Common questions include: How can I compute 95% confidence intervals for a median in SAS? How can I test whether the medians of two independent samples are significantly different? How can I repeat the previous analyses with other percentiles,

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The distribution of colors for plain M&M candies

February 20, 2017
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The distribution of colors for plain M&M candies

Many introductory courses in probability and statistics encourage students to collect and analyze real data. A popular experiment in categorical data analysis is to give students a bag of M&M® candies and ask them to estimate the proportion of colors in the population from the sample data. In some classes,

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An easy way to run thousands of regressions in SAS

February 13, 2017
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An easy way to run thousands of regressions in SAS

A common question on SAS discussion forums is how to repeat an analysis multiple times. Most programmers know that the most efficient way to analyze one model across many subsets of the data (perhaps each country or each state) is to sort the data and use a BY statement to

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Ten posts from 2016 that deserve a second look

January 11, 2017
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Ten posts from 2016 that deserve a second look

Last week I wrote about the 10 most popular articles from The DO Loop in 2016. The popular articles tend to be about elementary topics that appeal to a wide range of SAS programmers. Today I present an "editor's choice" list of technical articles that describe more advanced statistical methods

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