The analysis of variance (ANOVA) model can be extended from making a comparison between multiple groups to take into account additional factors in an experiment. The simplest extension is from one-way to two-way ANOVA where a second factor is included in the model as well as a potential interaction between the two factors. As an example
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Analysis of Variance (ANOVA) is a commonly used statistical technique for investigating data by comparing the means of subsets of the data. The base case is the one-way ANOVA which is an extension of two-sample t test for independent groups covering situations where there are more than two groups being compared. In one-way ANOVA the data
The grammar of graphics approach to constructing graphs has been implemented in the ggplot2 package in R. The author of the package, Hadley Wickham, has provided a website with many details of using the system to create nice looking graphics. The package removes many of the awkward parts of setting up graphical display that characterise other
A bar graph is a frequently used type of display that compares counts, frequencies, totals or other summary measures for a series of categories, e.g. sales in different market sectors or in quarters in a financial year. The bar graph can be laid out with the categories either on the vertical or horizontal axis of
The trellis graphics approach was pioneered by various statistical researchers and the ideas are used extensively in the book “Visualizing Data” by William Cleveland. There are various resources on the website for trellis graphics including S code for creating the majority of the graphs that appear in the book. Inspired by efforts on the Learning
One of the main strengths of the Trellis graphics paradigm is the use of panelling to divide data into subsets to investigate whether patterns are consistent as the conditioning variables change. In the ggplot2 package the terminology for specifying these separate panels is faceting and can be used to create similar displays. In our previous post
The ggplot2 package can be used as an alternative to lattice for producing high quality graphics in R. The package provides a framework and hopefully simple interface to producing graphs and is inspired by the grammar of graphics. The main function for producing graphs in this package is qplot, which stands for quick plot. The first
Zero Inflated Models and Generalized Linear Mixed Models with R.
Zuur, Saveliev, Ieno (2012).
