Analysis of Covariance – Extending Simple Linear Regression

April 28, 2010 | Ralph

The simple linear regression model considers the relationship between two variables and in many cases more information will be available that can be used to extend the model. For example, there might be a categorical variable (sometimes known as a covariate) that can be used to divide the data set ...
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Summarising data using box and whisker plots

April 25, 2010 | Ralph

A box and whisker plot is a type of graphical display that can be used to summarise a set of data based on the five number summary of this data. The summary statistics used to create a box and whisker plot are the median of the data, the lower and ...
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Simple Linear Regression

April 23, 2010 | Ralph

One of the most frequent used techniques in statistics is linear regression where we investigate the potential relationship between a variable of interest (often called the response variable but there are many other names in use) and a set of one of more variables (known as the independent variables or ...
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Summarising data using scatter plots

April 18, 2010 | Ralph

A scatter plot is a graph used to investigate the relationship between two variables in a data set. The x and y axes are used for the values of the two variables and a symbol on the graph represents the combination for each pair of values in the data set. ...
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Working with themes in Lattice Graphics

April 12, 2010 | Ralph

The Trellis graphics approach provides facilities for creating effective graphs with a consistent look and feel and one of the good things about the system is the use of themes to define the colour, size and other features of the components that make up a graph. The lattice package in ... [Read more...]

Summarising data using histograms

April 11, 2010 | Ralph

The histogram is a standard type of graphic used to summarise univariate data where the range of values in the data set is divided into regions and a bar (usually vertical) is plotted in each of these regions with height proportional to the frequency of observations in that region. In ... [Read more...]

Summarising data using dot plots

March 26, 2010 | Ralph

A dot plot is a type of display that compares counts, frequencies, totals or other summary measures for a series of categories. The dot plot can be arranged with the categories either on the vertical or horizontal axis of the display to allow comparising between the different categories as well ... [Read more...]

Summarising data using bar charts

December 12, 2009 | Ralph

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 ... [Read more...]

Graph Examples from Visualizing Data by William Cleveland

November 12, 2009 | Ralph

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 ... [Read more...]

Using Faceting in ggplot2 to create Trellis-like Plots

November 9, 2009 | Ralph

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 ... [Read more...]

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