Histogram

Histograms, BAR GRAPHS, and PIE CHARTS are used to display results in a simple, visual way. A bar chart would be used for categorical (nominal) variables, with each bar of the chart displaying the value of some variable. A histogram performs the [Page 462]same function for grouped data with an underlying CONTINUOUS VARIABLE (an ordinal, interval, or ratio distribution). The bars touch to reflect the continuous nature of the underlying distribution. A histogram or bar chart would be used in preference to a pie chart for showing trends across a variable (e.g., over time or by geographical locality). Pie charts are better for showing the percentage composition of a population.

Figure 1 shows the number of moves (changes of householder) recorded against properties where there has been a change of householder in the past year, in the center of a town in northeastern England that has been in decline since the collapse of its major industries but is now undergoing considerable regeneration. The figure shows nearly 150 properties that have had two changes of householder during the year and nontrivial numbers where ownership has been even more volatile. (The data for this figure are taken from Hobson-West & Sapsford, 2001.) As well as being descriptively useful, this kind of graph helps to determine the overall shape of the variable—the extent of departure from normality—which in this case is very substantial.

Figure 1 Number of Changes of Householder in Middlesbrough During 2001