Introduction

Charts and graphs are used to convey information in a way that a user can get an immediate overall impression about the data. It should be clear exactly what a chart or graph is about and so should have a fully descriptive heading or title if it is to be of any use.

Many students tend to be unsure of what type of graph or charts is appropriate and often use bar charts, just because they have more experience with them.

It is also clear that when using IT packages, such as Excel or OpenOffice, many tend to choose graphs that look good, regardless of whether they are appropriate or properly set up. They also do not give full attention to axes and scales. This is not good practice and will cost marks in coursework.

[In fact I suggest that you don’t use Excel to draw your graphs, unless you are prepared to spend time and effort doing them properly, you will find it easier and quicker to do the graphs manually on graph paper (not on ordinary paper for GCSE). I know this is heresy. However if you have a proper statistical package such as Fathom, Autograph, FX Draw/FX Stat, R,

Minitab or SPSS etc., then use that. It is also possible to get “Add Ins” for Excel, but I haven’t tried any of them. The examination boards do encourage the use of ICT to draw graphs though, but please be careful.]

Now, remember that data tends to split into three main types:

Qualitative (Categorical):

This is where the data is a type or category, types of make or colours or types of vehicle for instance.

Quantitative:

Discrete: This is where data is counted. Examples include how many blue cars, how many apples on a tree, how often did a person watch a particular TV programme.

Continuous: This is where data is measured, using some kind of measuring instrument. Examples include length, weight and mass, force, capacity, electrical quantities, etc.

Sometimes it isn’t obvious whether some data is discrete or continuous. For instance time or money can be considered as one or the other. It depends on how it is used. For instance you might count how many seconds elapse between two events.

If you allow fractions of a second to be appropriate then you should consider the time to be continuous, if fractions of a second are inappropriate then you might consider the time to be a discrete quantity. The same idea applies to dates. It depends upon what context you consider appropriate. Try to consider if it is meaningful or allowable to have fractions of the time or date?

For each type of data you have to use the correct types of graphs. This is now extremely important, especially for the GCSE Statistics examination.

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