Rick Wicklin, PhD, is a distinguished researcher in computational statistics at SAS and is a principal developer of SAS/IML software. His areas of expertise include computational statistics, simulation, statistical graphics, and modern methods in statistical data analysis. Rick is author of the books Statistical Programming with SAS/IML Software and Simulating Data with SAS.
Last week's post about odds ratio plots in SAS made me think about a similar plot that visualizes the parameter estimates for a regression analysis. The so-called regression coefficient plot is a scatter plot of the estimates for each effect in the model, with lines that indicate the width of
Imagine the following scenario. You have many data sets from various sources, such as individual stores or hospitals. You use the SAS DATA step to concatenate the many data sets into a single large data set. You give the big data set to a colleague who will analyze it. Later
Last week, SAS released the 14.1 version of its analytics products, which are shipped as part of the third maintenance release of 9.4. If you run SAS/IML programs from a 64-bit Windows PC, you might be interested to know that you can now create matrices with about 231 ≈ 2
I recently read an argument by Andrew Wheeler for using a logarithmic axis for plotting odds ratios. I found his argument convincing. Accordingly, this blog post shows how to create an odds ratio plot in SAS where the ratio axis is displayed on a log scale. Thanks to Bob Derr
Base SAS contains many functions for processing strings, and you can call these functions from within a SAS/IML program. However, sometimes a SAS/IML programmer needs to process a vector of strings. No problem! You can call most Base SAS functions with a vector of parameters. I have previously written about
The Raleigh News & Observer published a front-page article about the effect of wealth and poverty on high school athletics in North Carolina. In particular, the article concluded that "high schools with a high percentage of poor students rarely win titles in the so-called country club sports—tennis, golf and swimming—and
My colleague Robert Allison finds the most interesting data sets to visualize! Yesterday he posted a visualization of toothless seniors in the US. More precisely, he created graphs that show the estimated prevalence of adults (65 years or older) who have had all their natural teeth extracted. The dental profession
The triangular distribution has applications in risk analysis and reliability analysis. It is also a useful theoretical tool because of its simplicity. Its density function is piecewise linear. The standardized distribution is defined on [0,1] and has one parameter, 0 ≤ c ≤ 1, which determines the peak of the
A SAS programmer wanted to plot the normal distribution and highlight the area under curve that corresponds to the tails of the distribution. For example, the following plot shows the lower decile shaded in blue and the upper decile shaded in red. An easy way to do this in SAS
My son is in high school and plans to take the ACT, a standardized test to assess college aptitude and readiness. My wife asked, "What is a good score for the ACT?" I didn't know, but I did a quick internet search and discovered a tabulation of scores for the
Recently a SAS customer asked how to Winsorize data in SAS. Winsorization is best known as a way to construct robust univariate statistics. The Winsorized mean is a robust estimate of location. The Winsorized mean is similar to the trimmed mean, and both are described in the documentation for PROC
As my colleague Margaret Crevar recently wrote, it is useful to know how long SAS programs take to run. Margaret and others have written about how to use the SAS FULLSTIMER option to monitor the performance of the SAS system. In fact, SAS distributes a macro that enables you to
You've probably heard of a random walk, but have you heard about the drunkard's walk? I've previously written about how to simulate a one-dimensional random walk in SAS. In the random walk, you imagine a person who takes a series of steps where the step size and direction is a
SAS/IML software is used by many SAS programmers, primarily for creating custom algorithms and macros that implement statistical analyses that are not built into any SAS procedure. I know that PROC IML is used regularly by pharmaceutical companies, by the financial and insurance industries, and by researchers in medical colleges
When you count the outcomes of an experiment, you do not always observe all of the possible outcomes. For example, if you roll a six-sided die 10 times, it might be that the "1" face does not appear in those 10 rolls. Obviously, this situation occurs more frequently with small
When I am computing with SAS/IML matrices and vectors, I often want to label the columns or rows so that I can better understand the data. The labels are called headers, and the COLNAME= and ROWNAME= options in the SAS/IML PRINT statement enable you to add headers for columns and
In my article about finding an initial guess for root-finding algorithms, I stated that Newton's root-finding method "might not converge or might converge to a root that is far away from the root that you wanted to find." A reader wanted more information about that statement. I have previously shown
A SAS programmer asked an interesting question on a SAS Support Community. The programmer had a nonlinear function with 12 parameters. He also had file that contained 4,000 lines, where each line contained values for the 12 parameters. In other words, the file specified 4,000 different functions. The programmer wanted
One of the fundamental principles of computer programming is to break a task into smaller subtasks and to modularize the program by encapsulating each subtask into its own function. I have written many blog posts over the years about how to define and use functions in the SAS/IML language. I
A feature of SAS/IML 13.2 (shipped with SAS 9.4m2, Aug 2014) is the ability to execute SAS/IML statements that are in a file. The feature is implemented by the new EXECUTEFILE subroutine. This feature is similar to the CALL EXECUTE statement. The difference is that the EXECUTEFILE subroutine reads, parses,
"Daddy, help! Help me! Come quick!" I heard my daughter's screams from the upstairs bathroom and bounded up the stairs two at a time. Was she hurt? Bleeding? Was the toilet overflowing? When I arrived in the doorway, she pointed at the wall and at the floor. The wall was
Equations that involve trigonometric functions can have infinitely many solutions. For example, the solution to the equation tan(θ)=1 is θ = π/4 + kπ, where k is any integer. In order to obtain a unique solution to the equation, we define the "arc" functions: inverse trigonometric functions that return a
I still remember the first time I was asked to "consult" on a statistical problem. A former physics professor had some students who had gathered data that should lie along an arc of a theoretical circle. The professor asked if there was a regression technique that could find the center
I was reading a statistics book when I encountered a histogram that caught my eye. The histogram looked similar to the one at the left. It contained a normal density estimate overlaid on a histogram, but the height of the density curve seemed too short when compared to the heights
A SAS programmer asked for a list of SAS/IML functions that operate on the columns of an n x p matrix and return a 1 x p row vector of results. The functions that behave this way tend to compute univariate descriptive statistics such as the mean, median, standard deviation, and quantiles. The following
I previously wrote about the best way to suppress output from SAS procedures. Suppressing output is necessary in simulation and bootstrap analyses, and it is useful in other contexts as well. In my previous article, I wrote, "many programmers use ODS _ALL_ CLOSE as a way to suppress output, but
SAS procedures can produce a lot of output, but you don't always want to see it all. In simulation and bootstrap studies, you might analyze 10,000 samples or resamples. Usually you are not interested in seeing the results of each analysis displayed on your computer screen. Instead, you want to
When I was an undergraduate physic major, my favorite professor would start each class with a joke or pun. One day he began class with a paraphrase of a famous quote from the movie Star Trek 4: The Voyage Home (the one with the whales). "Today," my professor said, imitating
North Carolina is a state that requires yearly inspections of motor vehicles. An inspection checks for safety features (lights, brakes, tires,....) as well as checking vehicle emissions to ensure that vehicles meet air pollution standards. I recently had a car inspected and noticed a pie chart on the inspection's summary
Perhaps you saw the headlines earlier this week about the fact that it has been nine years since the last major hurricane (category 3, 4, or 5) hit the US coast. According to a post on the GeoSpace blog, which is published by the American Geophysical Union (AGU), researchers ran
