Histogram

Introduction

The histogram is a method that uses bars (rectangles) to represent the distribution (such as count or frequency, percentage, and proportion) of data by placing each data value in an appropriate class interval. It is very useful for examining how data are “spread”

Each rectangle in the histogram represents a class of data. The width of the rectangle corresponds to the width of the class interval. The independent variable consists of interval- or ratio-level data and is usually displayed on the x-axis, and the frequency data on the y-axis with the height of the bar proportional to the count.

Inputs

To illustrate this tool in use, we will examine the spread of the data for the MBS spend per capita across Brisbane’s suburbs. To do this:

  • Select Brisbane GCCSA as your area
  • Select SA2 OECD Indicators: MBS and PBS data as your dataset
  • Open the Histogram tool (Analyse → Tools → Charts → Histogram) and enter the following parameters as shown in the image below (Each of these are also explained below)
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  • Dataset Input: For this we want to select SA2 OECD Indicators: MBS and PBS data
  • Variable(s)The variables for which we would like to examine their spread. Here we select MBS spend per capita
  • Use Variable Titles: Check this box to have “human readable names” on your output chart
  • Chart Title: Here we enter the title for the plot. In this instance we have chosen Box Plot: MBS and PBS Spend per capita in Brisbane SA2s
  • Y-axis format: This allows us to choose how the Y-axis is formatted. The output histograms all look the same, but the y-axis can be formatted as density, frequency, percentage or proportion. Here we choose proportion
  •  Grid: Select this if you want to choose gridlines for your graph
  •  Greyscale: Select this if you want your graph to be in grey scale, rather than in the default colour

Once you have entered the parameters, click Add and Run

Outputs

Once your tool has run, click the Display button on the pop up dialogue box that appears

Your output should look something like the graph below. This indicates that the median MBS spend per capital is centred on $700-$800, with a long lower tail to the left

[Click to Enlarge]

References

(1) An Introduction to R (3.1.0 (2014-04-10)).
(2) Streiner, D. (2010) Histogram, N. Salkind (Ed.), Encyclopedia of research design, pp. 572 – 574, Thousand Oaks, CA: SAGE Publications, Inc.
(3) Dodge, Y. (2008) Histogram, The Concise Encyclopedia of Statistics, pp. 242 – 244, Springer, New York.
(4) Scott, D. W. (2010) Histogram, Wiley Interdisciplinary Reviews: Computational Statistics, Vol. 2, pp. 44 – 48, Wiley, New York.