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Bar chart of pairwise correlations between variables

Rick WicklinAugust 16, 2017 2

Use a bar chart to visualize pairwise correlations

Visualizing the correlations between variables often provides insight into the relationships between variables. I've previously written about how to use a heat map to visualize a correlation matrix in SAS/IML, and Chris Hemedinger showed how to use Base SAS to visualize correlations between variables. Recently a SAS programmer asked how

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Advanced Analytics | Data Visualization

Prediction regions for a classification problem with two outcomes. Graph created in SAS.

Rick WicklinJuly 17, 2017 0

3 ways to visualize prediction regions for classification problems

An important problem in machine learning is the "classification problem." In this supervised learning problem, you build a statistical model that predicts a set of categorical outcomes (responses) based on a set of input features (explanatory variables). You do this by training the model on data for which the outcomes

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Analytics | Data Visualization

Rick WicklinMay 24, 2017 7

Sample quantiles: A comparison of 9 definitions

According to Hyndman and Fan ("Sample Quantiles in Statistical Packages," TAS, 1996), there are nine definitions of sample quantiles that commonly appear in statistical software packages. Hyndman and Fan identify three definitions that are based on rounding and six methods that are based on linear interpolation. This blog post shows

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Analytics | Data Visualization

Distribution of Lead Levels in Flint, Michigan, in 71 Water Samples

Rick WicklinMay 17, 2017 11

Quantiles and the Flint water crisis

The April 2017 issue of Significance magazine features a cover story by Robert Langkjaer-Bain about the Flint (Michigan) water crisis. For those who don't know, the Flint water crisis started in 2014 when the impoverished city began using the Flint River as a source of city water. The water was

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Data Visualization

Perceived probabilities for word phrases

Rick WicklinMay 3, 2017 4

Perceptions of probability

If a financial analyst says it is "likely" that a company will be profitable next year, what probability would you ascribe to that statement? If an intelligence report claims that there is "little chance" of a terrorist attack against an embassy, should the ambassador interpret this as a one-in-a-hundred chance,

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Analytics | Data Visualization | Programming Tips

Rick WicklinApril 26, 2017 0

Visualize a design matrix

Most SAS regression procedures support a CLASS statement which internally generates dummy variables for categorical variables. I have previously described what dummy variables are and how are they used. I have also written about how to create design matrices that contain dummy variables in SAS, and in particular how to

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Analytics | Data Visualization

Rick WicklinApril 24, 2017 1

Visualize an ANOVA with two-way interactions

There are several ways to visualize data in a two-way ANOVA model. Most visualizations show a statistical summary of the response variable for each category. However, for small data sets, it can be useful to overlay the raw data. This article shows a simple trick that you can use to

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Data Visualization | Learn SAS

Rick WicklinApril 17, 2017 8

Visualize the 68-95-99.7 rule in SAS

A reader commented on last week's article about constructing symmetric intervals. He wanted to know if I created it in SAS. Yes, the graph, which illustrates the so-called 68-95-99.7 rule for the normal distribution, was created by using several statements in the SGPLOT procedure in Base SAS The SERIES statement

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Analytics | Data Visualization

Rick WicklinFebruary 20, 2017 48

The distribution of colors for plain M&M candies

Many introductory courses in probability and statistics encourage students to collect and analyze real data. A popular experiment in categorical data analysis is to give students a bag of M&M® candies and ask them to estimate the proportion of colors in the population from the sample data. In some classes,

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Advanced Analytics | Data Visualization

Rick WicklinJanuary 30, 2017 5

Automate the creation of a discrete attribute map

If you are a SAS programmer and use the GROUP= option in PROC SGPLOT, you might have encountered a thorny issue: if you use a WHERE clause to omit certain observations, then the marker colors for groups might change from one plot to another. This happens because the marker colors

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