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 each other. Read the rest of this entry »

# Design of Experiments – Power Calculations

November 18th, 2009Prior 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 power of a test for a fixed sample size. Read the rest of this entry »

# Graph Examples from Visualizing Data by William Cleveland

November 12th, 2009The 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 R blog to recreate the examples from Deepayan Sarkar’s book on lattice using **ggplot2** I have decide to undertake a similar exercise based on the scripts that have been made available for creating the graphs from the book. Read the rest of this entry »

# Using Faceting in ggplot2 to create Trellis-like Plots

November 9th, 2009One 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. Read the rest of this entry »

# Creating scatter plots using ggplot2

November 6th, 2009The **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. Read the rest of this entry »