Summarising data using dot plots

March 26th, 2010

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 as comparison within categories where there are multiple symbols used to denote say different years. Read the rest of this entry »

Measuring the length of time to run a function

March 16th, 2010

When writing R code it is useful to be able to assess the amount of time that a particular function takes to run. We might be interested in measuring the increase in time required by our function as the size of the data increases. Read the rest of this entry »

Contingency Tables – Fisher’s Exact Test

March 6th, 2010

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 »