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Programming Tips

Rick WicklinJuly 25, 2018 0

Color cells in a mosaic plot by deviation from independence

Back in SAS 9.3M2 (SAS/STAT 12.1), PROC FREQ introduced mosaic plots to visualize the joint frequencies in a contingency table. By default, the cells in a mosaic plot are colored according to levels of one of the categorical variables in the analysis. However, in 2013 I showed how you can

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Analytics | Learn SAS | Programming Tips

Rick WicklinJuly 23, 2018 6

How to use the %BOOT and %BOOTCI macros in SAS

Since the late 1990s, SAS has supplied macros for basic bootstrap and jackknife analyses. This article provides an example that shows how to use the %BOOT and %BOOTCI macros. The %BOOT macro generates a bootstrap distribution and computes basic statistics about the bootstrap distribution, including estimates of bias, standard error,

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Programming Tips

Rick WicklinJuly 18, 2018 0

Balanced bootstrap resampling in SAS

This article shows how to implement balanced bootstrap sampling in SAS. The basic bootstrap samples with replacement from the original data (N observations) to obtain B new samples. This is called "uniform" resampling because each observation has a uniform probability of 1/N of being selected at each step of the

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Data Visualization | Programming Tips

Rick WicklinJuly 16, 2018 1

Offset regions: Find all points within a specified distance from a polygon

My colleague Robert Allison recently blogged about using the diameter of Texas as a unit of measurement. The largest distance across Texas is about 801 miles, so Robert wanted to find the set of all points such that the distance from the point to Texas is less than or equal

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Programming Tips

Rick WicklinJuly 11, 2018 2

The probability that two random chords of a circle intersect

In a previous article, I showed how to find the intersection (if it exists) between two line segments in the plane. There are some fun problems in probability theory that involve intersections of line segments. One is "What is the probability that two randomly chosen chords of a circle intersect?"

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Analytics | Programming Tips

Rick WicklinJuly 9, 2018 3

The intersection of two line segments

Back in high school, you probably learned to find the intersection of two lines in the plane. The intersection requires solving a system of two linear equations. There are three cases: (1) the lines intersect in a unique point, (2) the lines are parallel and do not intersect, or (3)

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Analytics | Programming Tips

Rick WicklinJuly 5, 2018 7

Compute derivatives for nonparametric regression models

SAS enables you to evaluate a regression model at any location within the range of the data. However, sometimes you might be interested in how the predicted response is increasing or decreasing at specified locations. You can use finite differences to compute the slope (first derivative) of a regression model.

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Analytics | Programming Tips

Rick WicklinJune 27, 2018 2

Reduced models: A way to choose initial parameters for a mixed model

This article describes how to obtain an initial guess for nonlinear regression models, especially nonlinear mixed models. The technique is to first fit a simpler fixed-effects model by replacing the random effects with their expected values. The parameter estimates for the fixed-effects model are often good initial guesses for the

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Analytics | Programming Tips

Rick WicklinJune 20, 2018 11

The bootstrap method in SAS: A t test example

A previous article provides an example of using the BOOTSTRAP statement in PROC TTEST to compute bootstrap estimates of statistics in a two-sample t test. The BOOTSTRAP statement is new in SAS/STAT 14.3 (SAS 9.4M5). However, you can perform the same bootstrap analysis in earlier releases of SAS by using

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Programming Tips

Rick WicklinJune 15, 2018 2

Video: New random number generators in SAS

My 2018 SAS Global Forum paper was about "how to use the random-number generators (RNGs) in SAS." You can read the paper for details, but I recently recorded a short video that summarizes the main ideas in the paper. In particular, the video gives an overview of the new RNGs

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