## Bar Charts

### Simple Bar Charts

"A picture is worth a thousand words"

Bar charts are often used to illustrate data so that different categories can be compared.

The information is represented by a series of bars of the same width, displayed either vertically or horizontally. The height or length, respectively, represents the magnitude of the figures involved.

##### General Guidelines
1. Use vertical or horizontal bars; horizontal bars look better when long labels are being used.
2. Label both axes.
3. Put bars in a logical order, e.g. arranged by age, or date, or length of bar, etc. etc. (as appropriate).

### Grouped Bar Charts

These are just a development of the Simple Bar Chart type, except that 'natural grouping' is identified amongst the data.

Take note of a general guideline

• Don't have more than two or three bars in a grouped set unless absolutely necessary.

Here is an example with two bars in each grouped set

Comparisons of the Foot and Mouth Outbreaks in 1967 and 2001

### Stacked Bar Charts (Sectional Bar Charts)

The components of each bar in a stacked bar chart should show each component as a fraction (or percentage) of the whole.

Here is an example

Stacked bar chart showing the achievements of Formula 1 drivers in 2000

It is recommended that you consider using stacked bar charts rather than pie charts if you need to compare more than three sets of data.

### Words of Caution

Some opinions from Illinois University

Example quote :-

Two chart types that should always be avoided.

Two common charts easily produced by spreadsheet programs that should almost always be avoided are the stacked bar chart and the pie chart. The stacked bar chart, made even worse by the use of 3-D effects in figure 3, makes it very difficult to estimate the values of the variables represented on the top of the bars. Similar "stacking" can also been done with time series area charts and should be avoided as well.

### Microsoft Excel

Microsoft Excel differentiates between Bars (horizontal) and columns (vertical). We will not be making such a distinction here, they will all bars to us, whether horizontal or vertical..

You will see that Excel offers about half a dozen different 'varieties' of bar chart. We will not be explaining all these different types - we will explain the basic ideas of the fundamental types of chart.

In a few cases, a separate type of chart offered by Excel will, in reality, just be a slightly different form of a type of chart mentioned here.

Having said the above, this is only by way of explanation for when you specifically need to use a spreadsheet. For work on this Keyskills unit, we ask that you do not use Excel, or any other spreadsheet

## Past Exam Questions

#### The chart shows the number of late trains each day at Dunbridge for the weekdays 13-17 December 1999

A correct label for the vertical scale is

• A     Number of weekday trains per day
• B     Number of late trains per week
• C     Number of late trains per day
• D     Number of late trains