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Analytics | Data Visualization | Learn SAS

Rick WicklinDecember 14, 2020 5

A segmented regression model is a piecewise regression model that has two or more sub-models, each defined on a separate domain for the explanatory variables. For simplicity, assume the model has one continuous explanatory variable, X. The simplest segmented regression model assumes that the response is modeled by one parametric

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Analytics | Data Visualization

Rick WicklinDecember 7, 2020 3

Can you transplant an indoor Christmas tree?

"O Christmas tree, O Christmas tree, how lovely are your branches!" The idealized image of a Christmas tree is a perfectly straight conical tree with lush branches and no bare spots. Although this ideal exists only on Christmas cards, forest researchers are always trying to develop trees that approach the

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Analytics | Data Visualization | Programming Tips

Rick WicklinDecember 2, 2020 4

How to score a logistic regression model that was not fit by PROC LOGISTIC

A SAS customer asked a great question: "I have parameter estimates for a logistic regression model that I computed by using multiple imputations. How do I use these parameter estimates to score new observations and to visualize the model? PROC LOGISTIC can do the computation I want, but how do

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Analytics | Data Visualization

Rick WicklinNovember 23, 2020 4

Decile plots in SAS

I previously showed how to create a decile calibration plot for a logistic regression model in SAS. A decile calibration plot (or "decile plot," for short) is used in some fields to visualize agreement between the data and a regression model. It can be used to diagnose an incorrectly specified

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Analytics | Data Visualization

Predicted probabilities for a logistic regression model

Rick WicklinNovember 18, 2020 0

Create scoring data when regressors are correlated

To help visualize regression models, SAS provides the EFFECTPLOT statement in several regression procedures and in PROC PLM, which is a general-purpose procedure for post-fitting analysis of linear models. When scoring and visualizing a model, it is important to use reasonable combinations of the explanatory variables for the visualization. When

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Data Visualization | Learn SAS

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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