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Rick WicklinAugust 17, 2022 1

The Box-Cox transformation for a dependent variable in a regression

In the 1960s and '70s, before nonparametric regression methods became widely available, it was common to apply a nonlinear transformation to the dependent variable before fitting a linear regression model. This is still done today, with the most common transformation being a logarithmic transformation of the dependent variable, which fits

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Analytics | Data Visualization | Learn SAS

Rick WicklinAugust 15, 2022 0

Tukey's ladder of variable transformations

John Tukey was an influential statistician who proposed many statistical concepts. In the 1960s and 70s, he was fundamental in the discovery and exposition of robust statistical methods, and he was an ardent proponent of exploratory data analysis (EDA). In his 1977 book, Exploratory Data Analysis, he discussed a small

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Analytics | Learn SAS

Rick WicklinAugust 8, 2022 1

Means and medians as minimizers of a loss function

On Twitter, I saw a tweet from @DataSciFact that read, "The sum of (x_i - x)^2 over a set of data points x_i is minimized when x is the sample mean." I (@RickWicklin) immediately tweeted out a reply: "And the sum of |x_i - x| is minimized by the sample

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Rick WicklinAugust 3, 2022 0

How to examine the status of ODS destinations in SAS

A SAS programmer asked for help on a discussion forum: "My SAS session will not display any tables or graphs! I try to use PROC PRINT and other procedures, but no output is displayed! What can I do?" The most common reasons why you might not see any output when

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Analytics | Learn SAS

Rick WicklinAugust 1, 2022 0

Introductory examples of Monte Carlo simulation in SAS

When I was writing Simulating Data with SAS (Wicklin, 2013), I read a lot of introductory textbooks about Monte Carlo simulation. One of my favorites is Sheldon Ross's book Simulation. (I read the 4th Edition (2006); the 5th Edition was published in 2013.) I love that the book brings together

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Learn SAS | Programming Tips

Rick WicklinJuly 25, 2022 0

Monte Carlo estimates of area

I've previously shown how to use Monte Carlo simulation to estimate probabilities and areas. I illustrated the Monte Carlo method by estimating π ≈ 3.14159... by generating points uniformly at random in a unit square and computing the proportion of those points that were inside the unit circle. The previous

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Learn SAS | Programming Tips

Rick WicklinJuly 20, 2022 0

A tip for visualizing the density function of a distribution

It isn't easy to draw the graph of a function when you don't know what the graph looks like. To draw the graph by using a computer, you need to know the domain of the function for the graph: the minimum value (xMin) and the maximum value (xMax) for plotting

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Learn SAS | Programming Tips

Rick WicklinJuly 18, 2022 2

Tips for computing right-tail probabilities and quantiles

A colleague was struggling to compute a right-tail probability for a distribution. Recall that the cumulative distribution function (CDF) is defined as a left-tail probability. For a continuous random variable, X, with density function f, the CDF at the value x is F(x) = Pr(X ≤ x) = ∫

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Data Visualization | Learn SAS

Rick WicklinJuly 13, 2022 0

Use ODS to arrange graphs in a panel

A SAS programmer wanted to create a panel that contained two of the graphs side-by-side. The graphs were created by using calls to two different SAS procedures. This article shows how to select the graphs and arrange them side-by-side by using the ODS LAYOUT GRIDDED statement. The end of the

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Analytics | Learn SAS

Rick WicklinJuly 11, 2022 4

Confidence bands for partial leverage regression plots

I previously wrote about partial leverage plots for regression diagnostics and why they are useful. You can generate a partial leverage plot in SAS by using the PLOTS=PARTIALPLOT option in PROC REG. One useful property of partial leverage plots is the ability to graphically represent the null hypothesis that a

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