Analytics | Learn SAS | Programming Tips

Rick WicklinApril 17, 2023 0

Should you use the Wald confidence interval for a binomial proportion?

The "Teacher’s Corner" of The American Statistician enables statisticians to discuss topics that are relevant to teaching and learning statistics. Sometimes, the articles have practical relevance, too. Andersson (2023) "The Wald Confidence Interval for a Binomial p as an Illuminating 'Bad' Example," is intended for professors and masters-level students in

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Analytics

Rick WicklinApril 10, 2023 0

Means and medians of subgroups

A journal article listed the mean, median, and size for subgroups of the data, but did not report the overall mean or median. A SAS programmer wondered what, if any, inferences could be made about the overall mean and median for the data. The answer is that you can calculate

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Rick WicklinApril 5, 2023 0

Weak or strong? How to interpret a Spearman or Kendall correlation

A SAS user asked how to interpret a rank-based correlation such as a Spearman correlation or a Kendall correlation. These are alternative measures to the usual Pearson product-moment correlation, which is widely used. The programmer knew that words like "weak," "moderate," and "strong" are sometimes used to describe the Pearson

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Analytics | Learn SAS

Rick WicklinApril 3, 2023 0

Why use rank correlation?

A previous article discusses rank correlation and lists some advantages of using rank correlation. However, the article does not show examples where an analyst might prefer to report the rank correlation instead of the traditional Pearson product-moment correlation. This article provides three examples where the rank correlation is a better

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Learn SAS | Programming Tips

Rick WicklinMarch 29, 2023 0

Using SAS to solve an introductory programming assignment

I recently discussed introductory programming with a colleague who teaches Python at a university. He told me about the following introductory programming assignment: Let N be an integer parameter in the range [1, 9]. For each value of N, find all pairs of one-digit positive integers d1 and d2 that

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Analytics

Rick WicklinMarch 27, 2023 0

Simpson's paradox and confounding variables

A previous article discusses the issue of a confounding variable and uses correlation to give an example. The example shows that the correlation between two variables might be affected by a third variable, which is called a confounding variable. The article mentions that you can use the PARTIAL statement in

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Analytics | Learn SAS | Programming Tips

Rick WicklinMarch 22, 2023 0

Partial correlation: controlling for confounding variables

A data analyst wanted to estimate the correlation between two variables, but he was concerned about the influence of a confounding variable that is correlated with them. The correlation might affect the apparent relationship between main two variables in the study. A common confounding variable is age because young people

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Learn SAS | Programming Tips

Rick WicklinMarch 20, 2023 0

Estimate a Markov transition matrix from historical data

In a previous article about Markov transition matrices, I mentioned that you can estimate a Markov transition matrix by using historical data that are collected over a certain length of time. A SAS programmer asked how you can estimate a transition matrix in SAS. The answer is that you can

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Analytics | Learn SAS | Programming Tips

Rick WicklinMarch 15, 2023 0

Fitting a distribution to an expert's opinion: An application of the metalog distribution

Most homeowners know that large home improvement projects can take longer than you expect. Whether it's remodeling a kitchen, adding a deck, or landscaping a yard, big projects are expensive and subject to a lot of uncertainty. Factors such as weather, the availability of labor, and the supply of materials,

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Analytics | Learn SAS | Programming Tips

Rick WicklinMarch 13, 2023 0

Use the metalog distribution in SAS

A previous article describes the metalog distribution (Keelin, 2016). The metalog distribution is a flexible family of distributions that can model a wide range of shapes for data distributions. The metalog system can model bounded, semibounded, and unbounded continuous distributions. This article shows how to use the metalog distribution in

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Learn SAS | Programming Tips

Rick WicklinMarch 8, 2023 0

How Newton calculated pi to 16 decimal places

Happy Pi Day! Every year on March 14th (written 3/14 in the US), people in the mathematical sciences celebrate "all things pi-related" because 3.14 is the three-decimal approximation to π ≈ 3.14159265358979.... Modern computer methods and algorithms enable us to calculate 100 trillion digits of π. However, I think it

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Learn SAS | Programming Tips

Rick WicklinMarch 6, 2023 0

The variance of the sums of variables

Undergraduate textbooks on probability and statistics typically prove theorems that show how the variance of a sum of random variables is related to the variance of the original variables and the covariance between them. For example, the Wikipedia article on Variance contains an equation for the sum of two random

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Analytics | Programming Tips

Rick WicklinMarch 1, 2023 0

The distribution of the difference between two beta random variables

A SAS programmer wanted to compute the distribution of X-Y, where X and Y are two beta-distributed random variables. Pham-Gia and Turkkan (1993) derive a formula for the PDF of this distribution. Unfortunately, the PDF involves evaluating a two-dimensional generalized hypergeometric function, which is not available in all programming languages.

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Analytics | Programming Tips

Rick WicklinFebruary 27, 2023 0

Compute hypergeometric functions in SAS

In applied mathematics, there is a large collection of "special functions." These function appera in certain applications, often as the solution to a differential equation, but also in the definition of probability distributions. For example, I have written about Bessel functions, the complete and incomplete gamma function, and the complete

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Rick WicklinFebruary 22, 2023 0

What is the metalog distribution?

The metalog family of distributions (Keelin, Decision Analysis, 2016) is a flexible family that can model a wide range of continuous univariate data distributions when the data-generating mechanism is unknown. This article provides an overview of the metalog distributions. A subsequent article shows how to download and use a library

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Analytics | Learn SAS | Programming Tips

Rick WicklinFebruary 20, 2023 0

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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Data Visualization | Learn SAS | Programming Tips

Rick WicklinFebruary 8, 2023 0

A random walk inside a heart

SAS programmers love to make special graphs for Valentine's Day. In fact, there is a long history of heart-shaped graphs and love-inspired programs written in SAS! Last year, I added to the collection by showing how a ball bounces on a heart-shaped billiards table. This year, I create a similar

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Learn SAS | Programming Tips

Rick WicklinFebruary 6, 2023 0

How to use Git to share SAS programs

This article is about how to use Git to share SAS programs, specifically how to share libraries of SAS IML functions. Some IML programmers might remember an earlier way to share libraries of functions: SAS/IML released "packages" in SAS 9.4m3 (2015), which enable you to create, document, share, and use

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Data Visualization | Learn SAS | Programming Tips

Rick WicklinFebruary 1, 2023 0

Colorblind-safe palettes in SAS

SAS supports the ColorBrewer system of color palettes from the ColorBrewer website (Brewer and Harrower, 2002). The ColorBrewer color ramps are available in SAS by using the PALETTE function in SAS IML software. The PALETTE function supports all ColorBrewer palettes, but some palettes are not interpretable by people with color

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Data Visualization | Learn SAS | Programming Tips

Rick WicklinJanuary 30, 2023 0

Tips for making colorblind-safe statistical graphs

Did you know that about 8% of the world's men are colorblind? (More correctly, 8% of men are "color vision deficient," since they see colors, but not all colors.) Because of the "birthday paradox," in a room that contains eight men, the probability is 50% that at least one is

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Learn SAS | Programming Tips

Rick WicklinJanuary 25, 2023 0

Write to the log from SAS IML programs

I previously discussed how to use the PUTLOG statement to write a message from the DATA step to the log in SAS. The PUTLOG statement is commonly used to write notes, warnings, and errors to the log. This article shows how to use the PRINTTOLOG subroutine in SAS IML software

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Rick WicklinJanuary 23, 2023 0

Use the PUTLOG statement to write errors, warning, and notes to the SAS log

Many experienced SAS programmers use the PUT statement to write messages to the log from a DATA step. But did you know that SAS supports the PUTLOG function, which is another way to write a message to the log? I use the PUTLOG statement in the DATA step for the

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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 0

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 0

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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Rick WicklinDecember 19, 2022 0

Working with combinations in SAS

A colleague posted a Christmas-themed code snippet that shows how to use the DATA step in SAS to output all the possible ways that Santa can hitch up a team of reindeer to pull his sled. The assumption is that Rudolph must lead the team, and the remaining reindeer are

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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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