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Rick WicklinJanuary 31, 2022 0

The ERF and ERFC functions for statisticians

Recently, a SAS programmer commented about one of my blog posts. He said that he had found an alternative answer on another website. Whereas my answer was formulated in terms of the normal cumulative distribution function (CDF), the other answer used the ERF function. This article shows the relationship between

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Analytics | Learn SAS | Programming Tips

Rick WicklinJanuary 24, 2022 0

Estimate percentiles in SAS Viya

How can you estimate percentiles in SAS Viya? This article shows how to call the percentile action from PROC CAS to estimate percentiles of variables in a CAS data table. Percentiles and quantiles are essentially the same (the pth quantile is the 100*pth percentile for p in [0, 1]), so

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Analytics | Learn SAS | Programming Tips

Rick WicklinJanuary 10, 2022 0

12 blog posts from 2021 that deserve a second look

On this blog, I write about a diverse set of topics that are relevant to statistical programming and data visualization. In a previous article, I presented some of the most popular blog posts from 2021. The most popular articles often deal with elementary or familiar topics that are useful to

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Analytics | Data Visualization | Programming Tips

Rick WicklinJanuary 3, 2022 3

Top 10 posts from The DO Loop in 2021

Last year, I wrote almost 100 posts for The DO Loop blog. My most popular articles were about data visualization, statistics and data analysis, and simulation and bootstrapping. If you missed any of these gems when they were first published, here are some of the most popular articles from 2021:

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Analytics | Data Visualization

Rick WicklinDecember 15, 2021 0

A statistical palette of Christmas colors

Suppose you are creating a craft project for the Christmas holidays, and you want to choose a palette of Christmas colors to give it a cheery holiday appearance. You could use one of the many online collections of color palettes to choose a Christmas-themed palette. However, I didn't want to

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Analytics | Data Visualization

Rick WicklinDecember 13, 2021 5

A principal component analysis of color palettes

In a previous article, I visualized seven Christmas-themed palettes of colors, as shown to the right. You can see that the palettes include many red, green, and golden colors. Clearly, the colors in the Christmas palettes are not a random sample from the space of RGB colors. Rather, they represent

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Analytics | Programming Tips

Rick WicklinDecember 6, 2021 1

The expected number of points on a convex hull

While discussing how to compute convex hulls in SAS with a colleague, we wondered how the size of the convex hull compares to the size of the sample. For most distributions of points, I claimed that the size of the convex hull is much less than the size of the

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Analytics | Learn SAS

Rick WicklinDecember 1, 2021 2

Beware of repeated values in loess models

Did you know that the loess regression algorithm is not well-defined when you have repeated values among the explanatory variables, and you request a very small smoothing parameter? This is because loess regression at the point x0 is based on using the k nearest neighbors to x0. If x0 has

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Analytics | Data Visualization

Rick WicklinNovember 8, 2021 0

The normal approximation and random samples of the binomial distribution

Recall that the binomial distribution is the distribution of the number of successes in a set of independent Bernoulli trials, each having the same probability of success. Most introductory statistics textbooks discuss the approximation of the binomial distribution by the normal distribution. The graph to the right shows that the

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Analytics | Learn SAS

Rick WicklinNovember 1, 2021 1

Fit a mixture of Weibull distributions in SAS

A previous article discusses how to use SAS regression procedures to fit a two-parameter Weibull distribution in SAS. The article shows how to convert the regression output into the more familiar scale and shape parameters for the Weibull probability distribution, which are fit by using PROC UNIVARIATE. Although PROC UNIVARIATE

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