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Rick WicklinNovember 16, 2020 0

Three tips for plotting discontinuous functions in SAS

I have previously written about how to plot a discontinuous function in SAS. That article shows how to use the GROUP= option on the SERIES statement to graph a discontinuous function. An alternative approach is to place a missing value for the Y variable at the locations at which the

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Data Visualization | Learn SAS | Programming Tips

Rick WicklinNovember 11, 2020 2

Automate the placement of reference lines in PROC SGPLOT

The REFLINE statement in PROC SGPLOT is one of my favorite ways to augment statistical graphics such as scatter plots, series plots, and histograms. The REFLINE statement overlays a vertical or horizontal reference line on a graph. You can specify the location of the reference lines on the REFLINE statement.

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Data Visualization | Programming Tips

Decomposition of a convex polygon into triangles

Rick WicklinOctober 21, 2020 0

Generate random points in a polygon

The triangulation theorem for polygons says that every simple polygon can be triangulated. In fact, if the polygon has V vertices, you can decompose it into V-2 non-overlapping triangles. In this article, a "polygon" always means a simple polygon. Also, a "random point" means one that is drawn at random

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Analytics | Data Visualization

Rick WicklinOctober 14, 2020 1

A continuous band plot for visualizing uncertainty in regression predictions

A previous article discusses the confidence band for the mean predicted value in a regression model. The article shows a "graded confidence band plot," which I saw in Claus O. Wilke's online book, Fundamentals of Data Visualization (Section 16.3). It communicates uncertainty in the predictions. A graded band plot is

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Analytics | Data Visualization

Rick WicklinOctober 12, 2020 1

Visualize uncertainty in regression predictions

You've probably seen many graphs that are similar to the one at the right. This plot shows a regression line overlaid on a scatter plot of some data. Given a value for the independent variable (x), the regression line gives the best prediction for the mean of the response variable

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Analytics | Data Visualization | Learn SAS

Rick WicklinJuly 1, 2020 4

Pooled, within-group, and between-group covariance matrices

A previous article discusses the pooled variance for two or groups of univariate data. The pooled variance is often used during a t test of two independent samples. For multivariate data, the analogous concept is the pooled covariance matrix, which is an average of the sample covariance matrices of the

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Data Visualization | Programming Tips

Rick WicklinJune 22, 2020 0

Visualize the structure of a sparse matrix

Sometimes in matrix computations, it is important to display the nonzero elements of a matrix. This can be useful for visualizing the structure of a sparse matrix (one that has many zeros) and it is also useful when describing a matrix algorithm (such as Gaussian elimination) that introduces zeros at

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Analytics | Data Visualization

Rick WicklinMay 13, 2020 3

Find points where a regression curve has zero slope

This article shows how to find local maxima and maxima on a regression curve, which means finding points where the slope of the curve is zero. An example appears at the right, which shows locations where the loess smoother in a scatter plot has local minima and maxima. Except for

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Analytics | Data Visualization

Rick WicklinMay 6, 2020 3

What does 'flatten the curve' mean? To which curve does it apply?

During this coronavirus pandemic, there are many COVID-related graphs and curves in the news and on social media. The public, politicians, and pundits scrutinize each day's graphs to determine which communities are winning the fight against coronavirus. Interspersed among these many graphs is the oft-repeated mantra, "Flatten the curve!" As

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Analytics | Data Visualization

Rick WicklinApril 22, 2020 1

Visualize the case fatality rate for COVID-19 in US counties

A previous article describes the funnel plot (Spiegelhalter, 2005), which can identify samples that have rates or proportions that are much different than expected. The funnel plot is a scatter plot that plots the sample proportion of some quantity against the size of the sample. The variance of the sample

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