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Bar Chart

Bar chart
A bar chart displays the frequency of data using a serie of rectangles (bars). The information on a bar chart can be obtained from a frequency table, which displays both axes of the bar chart. It is one of the most common types of charts.

In a basic bar chart, ther is one bar for each value of the variable being illustrated. The length (or height) of the bar indicates the count, called the frequency of each value of the variable.

They are used in order to show numbers, proportions or other ratios. The variable which is described is qualitative or discrete.

The pupils in Mr. Smit's class take a Maths test and get scores out of 10, which are listed below:

2 4 5 6 2 8 1 7 8 10 6 5 7 0 2 3 9 10 1 6

They are asked to produce a vertical bar chart.

Step 1. Produce a frequency table.
This is a table showing the number of times each score appears.
For example, the score "6" appears 3 times, so the frequency of "6" is 3.

Score	Frequency
0	1
1	2
2	3
3	1
4	1
5	2
6	3
7	2
8	2
9	1
10	2

Step 2 . Draw the vertical bar chart.
In a vertical bar chart , the frequency always goes on the vertical axis.
The scores will be on the horizontal axis and there will be one vertical bar for each score.
The height of each score's vertical bar is given by the frequency of that score.
Don't forget to label both axis and give the graph a tittle.

Orientation of the bar chart
Bar charts can be either vertical, with the bars running up and down, or horizontal, with the bars running side to side.

Vertical bar chart

Horizontal bar chart

There are at least two types of bar chart which can be used: a multiple bar chart and a compound (or component or stacked) bar chart. Let's see them.

Multiple bar charts
A multiple bar chart is a different way of showing the relationship between two variables.
This chart consists of groups of two or more adjacents bars separated from the next group by a gap having, ideally, a different width to the bars themselves.
The diagram may be horizontal or vertical with the values either specified on the diagram or indicated using a standard axis.

The following are percentage distributions of household income in two regions:

Income ($'000)	Region A	Region B
0-10	20	10
10-20	30	20
20-30	35	30
30-40	10	20
40 or more	5	20
Total	100	100

Display the data by a multiple bar chart.

Compound (or component or stacked) bar chart.
In a compound bar chart the length of the complete bar signifies 100% of the population. The bar is subdivided into sections that show the relative sizes of components of population. By comparing the sizes of the subdivisions of two parallel compound bars, differences can be seen between the compositions of separate populations.

The following information shows the favourite subjects of students at a college:

Favourite subject	Girls	Boys
Mathematics	10	15
Science	5	10
Languages	15	5
Arts	20	10

Illustrate this information as a compound bar chart