Bar Chart

History

The creation of the first bar chart is attributed to William Playfair and appeared in The Commercial and Political Atlas in 1786. Playfair's bar graph was an adaptation of Joseph Priestley's time-line charts, which were popular at the time. Ironically, Playfair attributed his creation of the bar graph to a lack of data. In his Atlas, Playfair presented 34 plates containing line graphs or surface charts graphically representing the imports and exports from different countries over the years. Since he lacked the necessary time-series data for Scotland, he was forced to graph its trade data for a single year as a series of 34 bars, one for each of the imports and exports of Scotland's 17 trading partners. However, his innovation was largely ignored in Britain for a number of years. Playfair himself attributed little value to his invention, apologizing for what he saw as the limitations of the bar chart. It was not until 1801 and the publication of his Statistical Breviary that Playfair recognized the value of his invention. Playfair's invention fared better in Germany and France. In 1811 the German Alexander von Humboldt published adaptations of Playfair's bar graph and pie charts in Essai Politique sur le Royaume de la Nouvelle Espagne. In 1821, Jean Baptiste Joseph Fourier adapted the bar chart to create the first graph of cumulative frequency distribution, referred to as an ogive. In 1833, A. M. Guerry used the bar chart to plot crime data, creating the first histogram. Finally, in 1859 Playfair's work began to be accepted in Britain when Stanley Jevons published bar charts in his version of an economic atlas modeled on Playfair's earlier work. Jevons in turn influenced Karl Pearson, commonly considered the “father of modern statistics,” who promoted the widespread acceptance of the bar chart and other forms of information graphics.

Types

Although the terms bar chart and bar graph are now used interchangeably, the term bar chart was reserved traditionally for corresponding displays that did not have scales, grid lines, or tick marks. [Page 58]The value each bar represented was instead shown on or adjacent to the data graphic.

Figure 1 Simple Bar Chart and Associated Data

Note: USD= U.S. dollars.

An example bar chart is presented in Figure 1. Bar charts can display data by the use of either horizontal or vertical bars; vertical bar charts are also referred to as column graphs. The bars are typically of a uniform width with a uniform space between bars. The end of the bar represents the value of the category being plotted. When there is no space between the bars, the graph is referred to as a joined bar graph and is used to emphasize the differences between conditions or discrete categories. When continuous quantitative scales are used on both axes of a joined bar chart, the chart is referred to as a histogram and is often used to display the distribution of variables that are of interval or ratio scale. If the widths of the bars are not uniform but are instead used to display some measure or characteristic of the data element represented by the bar, the graph is referred to as an area bar graph (see Figure 2). In this graph, the heights of the bars represent the total earnings in U.S. dollars, and the widths of the bars are used to represent the percentage of the earnings coming from exports. The information expressed by the bar width can be displayed by means of a scale on the horizontal axis or by a legend, or, as in this case, the values might be noted directly on the graph. If both positive and negative values are plotted on the quantitative axis, the graph is called a deviation graph. On occasion the bars are replaced with pictures or symbols to make the graph more attractive or to visually represent the data series; these graphs are referred to as pictographs or pictorial bar graphs.

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