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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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Analytics | Learn SAS

Rick WicklinAugust 14, 2017 7

What is rank correlation?

When someone refers to the correlation between two variables, they are probably referring to the Pearson correlation, which is the standard statistic that is taught in elementary statistics courses. Elementary courses do not usually mention that there are other measures of correlation. Why would anyone want a different estimate of

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Analytics

Rick WicklinJuly 19, 2017 1

A quantile definition for skewness

Skewness is a measure of the asymmetry of a univariate distribution. I have previously shown how to compute the skewness for data distributions in SAS. The previous article computes Pearson's definition of skewness, which is based on the standardized third central moment of the data. Moment-based statistics are sensitive to

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Analytics | Programming Tips

Rick WicklinJuly 5, 2017 7

Test for the equality of two proportions in SAS

A SAS customer asked how to use SAS to conduct a Z test for the equality of two proportions. He was directed to the SAS Usage Note "Testing the equality of two or more proportions from independent samples." The note says to "specify the CHISQ option in the TABLES statement

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Analytics

Rick WicklinJune 19, 2017 4

How to find a feasible point for a constrained optimization in SAS

Most numerical optimization routines require that the user provides an initial guess for the solution. I have previously described a method for choosing an initial guess for an optimization, which works well for low-dimensional optimization problems. Recently a SAS programmer asked how to find an initial guess when there are

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Analytics | Programming Tips

Rick WicklinJune 14, 2017 21

Two ways to compute maximum likelihood estimates in SAS

In a previous article, I showed two ways to define a log-likelihood function in SAS. This article shows two ways to compute maximum likelihood estimates (MLEs) in SAS: the nonlinear optimization subroutines in SAS/IML and the NLMIXED procedure in SAS/STAT. To illustrate these methods, I will use the same data

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Analytics | Programming Tips

Log-likelihood function for the binomial distribution

Rick WicklinJune 12, 2017 3

Two simple ways to construct a log-likelihood function in SAS

Maximum likelihood estimation (MLE) is a powerful statistical technique that uses optimization techniques to fit parametric models. The technique finds the parameters that are "most likely" to have produced the observed data. SAS provides many tools for nonlinear optimization, so often the hardest part of maximum likelihood is writing down

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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 | Learn SAS

Visualization of percentile definitions in SAS

Rick WicklinMay 22, 2017 1

Quantile definitions in SAS

In last week's article about the Flint water crisis, I computed the 90th percentile of a small data set. Although I didn't mention it, the value that I reported is different from the the 90th percentile that is reported in Significance magazine. That is not unusual. The data only had

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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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