A contingency table is used in statistics to provide a tabular summary of categorical data and the cells in the table are the number of occassions that a particular combination of variables occur together in a set of data. The relationship between variables in a contingency table are often investigated using Chi-squared tests. Read the rest of this entry »
Contingency Tables – Fisher’s Exact Test
March 6th, 2010Design of Experiments – Block Designs
February 20th, 2010In many experiments where the investigator is comparing a set of treatments there is the possibility of one or more sources of variability in the experimental measurements that can be accounted for during the design stage of the experimentation. For example we might be investigating four different pieces of machinery using say two different operators, who would be expected to display different degrees of competence with the equipment. Or we might not be able to run all of the experimental combinations in one session so we would want to take into account systematic differences that are due to experiments in the various sessions. Read the rest of this entry »
Two-way Analysis of Variance (ANOVA)
February 15th, 2010The 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. Read the rest of this entry »
One-way ANOVA (cont.)
February 12th, 2010In a previous post we considered using R to fit one-way ANOVA models to data. In this post we consider a few additional ways that we can look at the analysis. Read the rest of this entry »
One-way Analysis of Variance (ANOVA)
February 3rd, 2010Analysis 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. Read the rest of this entry »
Codecogs – Open-Source library of numerical components
January 8th, 2010The Codecogs website provides an Open-source library of functions for numerical analysis. One interesting component available on the website is the LaTeX equation editor which can be used to create graphics files of equations to include on webpages. Read the rest of this entry »
R Blogs
December 17th, 2009There are many blogs on Statistics, R and other related topics scattered around the internet. The R bloggers website provides a central hub where feeds from participating blogs are collated so that they can be viewed from a single website. Read the rest of this entry »
The Grammar of Graphics: ggplot2 package
December 14th, 2009The 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. Read the rest of this entry »
Design of Experiments – Blocking and Full Factorial Experimental Design Plans
December 6th, 2009When 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 data collected during the experiment. Read the rest of this entry »
