Displaying small counts
When the range of values in a discrete data set is small, is it possible to draw a histogram with each class containing only a single possible value — (0.5 to 1.5), (1.5 to 2.5), (2.5 to 3.5), etc. These classes are centred on the possible values in the data set (i.e. 1, 2, 3, etc).
Such a histogram can be improved by narrowing the rectangles so that they do not touch, since this emphasises the discrete nature of the data. The resulting display is called a bar chart of the data.
For discrete data, bar charts are preferable to histograms, provided this does not result in too many classes.
Hurricanes in the North Atlantic
A shipping company wants to assess the risk of delays to container ships crossing the North Atlantic. A contributing factor is the weather — severe storms can cause sailings to be cancelled or diverted. The table below shows the numbers of hurricanes in the North Atlantic each year between 1910 and 2009.
Decade | Year | |||||||||
---|---|---|---|---|---|---|---|---|---|---|
Beginning | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 |
3 4 2 4 11 4 5 9 8 8 |
3 4 2 4 8 8 6 7 4 9 |
4 2 6 4 6 3 3 2 4 4 |
3 3 9 5 6 7 4 3 4 7 |
0 5 6 7 6 6 4 5 3 9 |
4 1 5 5 9 4 6 7 11 15 |
11 8 7 3 4 7 6 4 9 5 |
2 4 3 5 3 6 5 3 3 5 |
3 4 3 6 7 5 5 5 10 8 |
1 3 3 7 7 12 5 7 8 3 |
The diagram below shows a histogram of the data.
Use the slider to change the display into a bar chart — the best display of the data.