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Analytics | Learn SAS | Programming Tips

Rick WicklinFebruary 20, 2023 2

Simulate from a bounded distribution that has a specified mean

A SAS programmer asked for help to simulate data from a distribution that has certain properties. The distribution must be supported on the interval [a, b] and have a specified mean, μ, where a < μ < b. It turns out that there are infinitely many distributions that satisfy these

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Analytics | Programming Tips

Rick WicklinFebruary 13, 2023 0

Estimate the pth root of a Markov transition matrix

You can use a Markov transition matrix to model the transition of an entity between a set of discrete states. A transition matrix is also called a stochastic matrix. A previous article describes how to use transition matrices for stochastic modeling. You can estimate a Markov transition matrix by using

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Analytics | Data Visualization | Learn SAS

Rick WicklinJanuary 18, 2023 0

Visualize how parameters in a binary logistic regression model affect the probability of the event

A previous article shows that you can use the Intercept parameter to control the ratio of events to nonevents in a simulation of data from a logistic regression model. If you decrease the intercept parameter, the probability of the event decreases; if you increase the intercept parameter, the probability of

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Analytics | Programming Tips

Rick WicklinJanuary 16, 2023 1

Simulate data from a logistic regression model: How the intercept parameter affects the probability of the event

This article shows that you can use the intercept parameter to control the probability of the event in a simulation study that involves a binary logistic regression model. For simplicity, I will simulate data from a logistic regression model that involves only one explanatory variable, but the main idea applies

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Analytics | Learn SAS | Programming Tips

Rick WicklinJanuary 11, 2023 2

12 blog posts from 2022 that deserve a second look

In a previous article, I presented some of the most popular blog posts from 2022. In general, popular articles deal with elementary topics that have broad appeal. However, I also write articles about advanced topics. The following articles didn't make the Top 10 list, but they deserve a second look.

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Analytics | SAS Administrators

Rick WicklinJanuary 9, 2023 0

Installing R for SAS IML in SAS Viya

Since 2008, SAS has supported an interface for calling R from the SAS/IML matrix language. Many years ago, I wrote blog posts that describe how to call R from PROC IML. For SAS 9.4, the process of installing R and calling R from PROC IML is documented in the SAS/IML

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Analytics | Learn SAS | Programming Tips

Rick WicklinJanuary 4, 2023 0

Top 10 posts from The DO Loop in 2022

Last year, I wrote almost 90 articles for The DO Loop blog. My most popular articles were about SAS programming, data visualization, statistics and data analysis, and matrix computations. If you missed these articles when I published them—or if you want to read them again!— here is the "Reader's Choice

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Analytics | Learn SAS | Programming Tips

Rick WicklinDecember 14, 2022 0

Construct heterogeneous structured covariance matrices in SAS

A previous article describes how to use SAS IML software to construct common covariance structures that are encountered in mixed models. Each covariance matrix has several parameters, and you want to construct a matrix for any choice of the parameters. After you have constructed the covariance matrix, you can use

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Analytics | Programming Tips

Rick WicklinNovember 21, 2022 0

The area under a piecewise linear curve

Recently, I needed to know "how much" of a piecewise linear curve is below the X axis. The coordinates of the curve were given as a set of ordered pairs (x1,y1), (x2,y2), ..., (xn, yn). The question is vague, so the first step is to define the question better. Should

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Analytics | Data Visualization | Programming Tips

Rick WicklinNovember 16, 2022 3

Optimal linear profile plots in SAS

A profile plot is a way to display multivariate values for many subjects. The optimal linear profile plot was introduced by John Hartigan in his book Clustering Algorithms (1975). In Michael Friendly's book (SAS System for Statistical Graphics, 1991), Friendly shows how to construct an optimal linear profile by using

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