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Data Visualization

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Rick WicklinApril 1, 2020 6

Estimates of doubling time for exponential growth

During an epidemic, such as the coronavirus pandemic of 2020, the media often shows graphs of the cumulative numbers of confirmed cases for different countries. Often these graphs use a logarithmic scale for the vertical axis. In these graphs, a straight line indicates that new cases are increasing at an

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Data Visualization | Learn SAS

Rick WicklinMarch 30, 2020 0

Smokestack plots: A visualization technique for comparing cumulative curves

A cumulative curve shows the total amount of some quantity at multiple points in time. Examples include: Total sales of songs, movies, or books, beginning when the item is released. Total views of blog posts, beginning when the post is published. Total cases of a disease for different countries, beginning

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Data Visualization

Rick WicklinMarch 25, 2020 11

How to read a cumulative frequency graph

During an outbreak of a disease, such as the coronavirus (COVID-19) pandemic, the media shows daily graphs that convey the spread of the disease. The following two graphs appear frequently: New cases for each day (or week). This information is usually shown as a histogram or needle plot. The graph

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Data Visualization | Learn SAS

Rick WicklinMarch 23, 2020 9

Add custom tick marks to a SAS graph

When you create a graph by using the SGPLOT procedure in SAS, usually the default tick locations are acceptable. Sometimes, however, you might want to specify a set of custom tick values for one or both axes. This article shows three examples: Specify evenly spaced values. Specify tick values that

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Advanced Analytics | Data Visualization | Programming Tips

Rick WicklinMarch 9, 2020 2

ROC curves for a binormal sample

In a previous article, I discussed the binormal model for a binary classification problem. This model assumes a set of scores that are normally distributed for each population, and the mean of the scores for the Negative population is less than the mean of scores for the Positive population. I

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Data Visualization | Learn SAS

Rick WicklinMarch 2, 2020 0

Create a deviation plot to visualize values relative to a baseline

A colleague recently posted an article about how to use SAS Visual Analytics to create a circular graph that displays a year's worth of temperature data. Specifically, the graph shows the air temperature for each day in a year relative to some baseline temperature, such as 65F (18C). Days warmer

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Analytics | Data Visualization

Rick WicklinFebruary 26, 2020 0

The binormal model for ROC curves

The ROC curve is a graphical method that summarizes how well a binary classifier can discriminate between two populations, often called the "negative" population (individuals who do not have a disease or characteristic) and the "positive" population (individuals who do have it). As shown in a previous article, there is

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Analytics | Data Visualization

Rick WicklinFebruary 17, 2020 2

Visualize collinearity diagnostics

A previous article shows how to interpret the collinearity diagnostics that are produced by PROC REG in SAS. The process involves scanning down numbers in a table in order to find extreme values. This can be a tedious and error-prone process. Friendly and Kwan (2009) compare this task to a

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Analytics | Data Visualization | Learn SAS

Rick WicklinFebruary 5, 2020 6

Visualize residual projections for linear regression

A SAS programmer wanted to create a graph that illustrates how Deming regression differs from ordinary least squares regression. The main idea is shown in the panel of graphs below. The first graph shows the geometry of least squares regression when we regress Y onto X. ("Regress Y onto X"

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Analytics | Data Visualization | Programming Tips

Rick WicklinJanuary 27, 2020 4

The Johnson SU distribution

The Johnson system (Johnson, 1949) contains a family of four distributions: the normal distribution, the lognormal distribution, the SB distribution (which models bounded distributions), and the SU distribution (which models unbounded distributions). Note that 'B' stands for 'bounded' and 'U' stands for 'unbounded.' A previous article explains the purpose of

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