Math Statistics: Bar Charts/Bar Graphs

A bar chart represents the data as horizontal or vertical bars. The length of each bar is proportional to the amount that it represents.

There are 3 main types of bar charts.

• Vertical bar chart
• Horizontal bar chart
• Double bar chart

When constructing a bar chart it is important to choose a suitable scale to represent the frequency.

Example :

The following table shows the number of visitors to a park for the months January to March.

a) Construct a vertical and a horizontal bar chart for the table.

b) What is the percentage of increase of visitors to the park in March compared to January?

c) What percentage of visitors came in February compared with total number of visitors over the three months?

Solution:

a) If we choose a scale of 1:50 for the frequency then the vertical bar chart and horizontal bar chart will be as shown.

b) Increase in March compared to January is

c) Percentage of visitors in February compared to the total number of visitors is

DOUBLE BAR CHART

The double bar chart is used when we want to represent two sets of data on the same chart. We can put the bars side by side or we may put the bars of one set of data on top of the bars of the other set of data.

The choice of the forms of double bar chart – side by side or stacked, depends on the main purpose of the chart. A side by side chart is more useful when we compare the two sets of data (example: the number of adult visitors as compared to the number of child visitors); whereas the stacked chart emphasizes the totals of the two sets of data (example: total number of visitors).

Example :

The following frequency graph shows the number of adult visitors and child visitors to a park. Construct a side by side double bar chart and a stacked double bar chart for the frequency table.

Solution:

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