# Articles by Ralph

### Summarising data using bar charts

December 12, 2009 |

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...]

### Design of Experiments – Blocking and Full Factorial Experimental Design Plans

December 6, 2009 |

When considering using a full factorial experimental design there may be constraints on the number of experiments that can be run during a particular session, or there may be other practical constraints that introduce systematic differences into an experiment that can be handled during the design and analysis of the ... [Read more...]

### Design of Experiments – Full Factorial Designs

December 1, 2009 |

In designs where there are multiple factors, all with a discrete group of level settings, the full enumeration of all combinations of factor levels is referred to as a full factorial design. As the number of factors increases, potentially along with the settings for the factors, the total number of ... [Read more...]

### Design of Experiments – Optimal Designs

November 29, 2009 |

When designing an experiment it is not always possible to generate a regular, balanced design such as a full or fractional factorial design plan. There are usually restrictions of the total number of experiments that can be undertaken or constraints on the factor settings both individually or in combination with ... [Read more...]

### Design of Experiments – Power Calculations

November 18, 2009 |

Prior to conducting an experiment researchers will often undertake power calculations to determine the sample size required in their work to detect a meaningful scientific effect with sufficient power. In R there are functions to calculate either a minimum sample size for a specific power for a test or the ... [Read more...]

### Graph Examples from Visualizing Data by William Cleveland

November 12, 2009 |

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 |

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...]

### Creating scatter plots using ggplot2

November 6, 2009 |

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 ... [Read more...]

### Investigation the relationship between two variables using a scatter plot

October 13, 2009 |

The relationship between two variables can be visually represented using a scatter plot and will provide some insight into the correlation between the variables and possible models to describe the relationship. There are different ways to produce scatter plots in R making use of either the base graphics system, the ... [Read more...]
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