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Rick WicklinApril 27, 2020 2

I've previously written about how to generate points that are uniformly distributed in the unit disk. A seemingly unrelated topic is the distribution of eigenvalues (in the complex plane) of various kinds of random matrices. However, I recently learned that these topics are somewhat related! A mathematical result called the

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Learn SAS | Programming Tips

Rick WicklinMarch 18, 2020 4

Print SAS/IML variables with formats

A SAS/IML programmer asked about the best way to print multiple SAS/IML variables when each variable needs a different format. He wanted the output to resemble the "Parameter Estimates" table that is produced by PROC REG and other SAS/STAT procedures. This article shows four ways to print SAS/IML vectors in

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Analytics | Programming Tips

Rick WicklinMarch 16, 2020 2

Predict a random integer: The tradeoff between bias and variance

Books about statistics and machine learning often discuss the tradeoff between bias and variance for an estimator. These discussions are often motivated by a sophisticated predictive model such as a regression or a decision tree. But the basic idea can be seen in much simpler situations. This article presents a

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Advanced Analytics | Data Visualization | Programming Tips

Rick WicklinMarch 9, 2020 2

ROC curves for a binormal sample

In a previous article, I discussed the binormal model for a binary classification problem. This model assumes a set of scores that are normally distributed for each population, and the mean of the scores for the Negative population is less than the mean of scores for the Positive population. I

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Learn SAS | Programming Tips

Rick WicklinMarch 4, 2020 0

Store pre-computed matrices in a list

Suppose that a data set contains a set of parameter values. For each row of parameters, you need to perform some computation. A recent discussion on the SAS Support Communities mentions an important point: if there are duplicate rows in the data, a program might repeat the same computation several

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Programming Tips

Rick WicklinFebruary 24, 2020 5

Visualization of a binary classification analysis

The purpose of this article is to show how to use SAS to create a graph that illustrates a basic idea in a binary classification analysis, such as discriminant analysis and logistic regression. The graph, shown at right, shows two populations. Subjects in the "negative" population do not have some

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Learn SAS | Programming Tips

Rick WicklinFebruary 19, 2020 3

A list of SAS DATA step functions that do not run in CAS

Are you a statistical programmer whose company has adopted SAS Viya? If so, you probably know that the DATA step can run in parallel in SAS Cloud Analytic Services (CAS). As Sekosky (2017) says, "running in a single thread in SAS is different from running in many threads in CAS."

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Analytics | Learn SAS | Programming Tips

Rick WicklinFebruary 12, 2020 0

The Johnson system: Which distribution should you choose to model data?

The Johnson system (Johnson, 1949) contains a family of four distributions: the normal distribution, the lognormal distribution, the SB distribution, and the SU distribution. Previous articles explain why the Johnson system is useful and show how to use PROC UNIVARIATE in SAS to estimate parameters for the Johnson SB distribution

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Learn SAS | Programming Tips $Find the fractional part of a number$

Rick WicklinFebruary 10, 2020 1

Find the fractional part of a number

You can represent every number as a nearby integer plus a decimal. For example, 1.3 = 1 + 0.3. The integer is called the integer part of x, whereas the decimal is called the fractional part of x (or sometimes the decimal part of x). This representation is not unique.

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Programming Tips

Rick WicklinFebruary 3, 2020 4

What sample size do you need for a binomial test of proportions?

Recently someone on social media asked, "how can I compute the required sample size for a binomial test?" I assume from the question that the researcher was designing an experiment to test the proportions between two groups, such as a control group and a treatment/intervention group. They wanted to know

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