Posts Tagged ‘ data analysis ’

The diffogram and other graphs for multiple comparisons of means

October 18, 2017
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The diffogram and other graphs for multiple comparisons of means

In a previous article, I discussed the lines plot for multiple comparisons of means. Another graph that is frequently used for multiple comparisons is the diffogram, which indicates whether the pairwise differences between means of groups are statistically significant. This article discusses how to interpret a diffogram. Two related plots

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Graphs for multiple comparisons of means: The lines plot

October 16, 2017
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Graphs for multiple comparisons of means: The lines plot

Last week Warren Kuhfeld wrote about a graph called the "lines plot" that is produced by SAS/STAT procedures in SAS 9.4M5. (Notice that the "lines plot" has an 's'; it is not a line plot!) The lines plot is produced as part of an analysis that performs multiple comparisons of

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Order correlations by magnitude

October 9, 2017
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Order correlations by magnitude

Correlations between variables are typically displayed in a matrix. Because the correlation matrix is determined by the order of the variables, it is difficult to find the largest and smallest correlations, which is why analysts sometimes use colors to visualize the correlation matrix. Another visualization option is the pairwise correlation

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Create and interpret a weighted histogram

October 4, 2017
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Create and interpret a weighted histogram

If you perform a weighted statistical analysis, it can be useful to produce a statistical graph that also incorporates the weights. This article shows how to construct and interpret a weighted histogram in SAS. How to construct a weighted histogram Before constructing a weighted histogram, let's review the construction of

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How to understand weight variables in statistical analyses

October 2, 2017
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How to understand weight variables in statistical analyses

How can you specify weights for a statistical analysis? Hmmm, that's a "weighty" question! Many people on discussion forums ask "What is a weight variable?" and "How do you choose a weight for each observation?" This article gives a brief overview of weight variables in statistics and includes examples of

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Fisher’s transformation of the correlation coefficient

September 20, 2017
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Fisher’s transformation of the correlation coefficient

Pearson's correlation measures the linear association between two variables. Because the correlation is bounded between , the sampling distribution for highly correlated variables is highly skewed. Even for bivariate normal data, the skewness makes it challenging to estimate confidence intervals for the correlation, to run one-sample hypothesis tests ("Is

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Construct polynomial effects in SAS regression models

September 7, 2017
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If you use SAS regression procedures, you are probably familiar with the "stars and bars" notation, which enables you to construct interaction effects in regression models. Although you can construct many regression models by using that classical notation, a friend recently reminded me that the EFFECT statement in SAS provides

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7 ways to view correlation

September 5, 2017
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Correlation is a fundamental statistical concept that measures the linear association between two variables. There are multiple ways to think about correlation: geometrically, algebraically, with matrices, with vectors, with regression, and more. To paraphrase the great songwriter Paul Simon, there must be 50 ways to view your correlation! But don't

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