A categoric variable has values which are described by labels. When you present the result of an investigation like this, you should not plot the results on a line graph; you must use a bar chart or pie chart. For example: If you investigate the effect of acid on different metals, e.g. copper, zinc and iron, the type of metal you are using is a categoric variable. e.g. Chris is investigating the average fuel efficiency of different cars. He creates the following categories: city, small family, family, estate and people carrier. He then finds data from various manufacturers and calculates an average for each category. A line graph of this data is not very useful because there isn't such a thing as a car which is a bit bigger than a city car, but smaller than a small family car. These categories are also quite arbitrary: it's difficult in some cases to categorise cars. A bar chart is probably most useful in this case as it allows a quick comparison to be made at a glance.
Image source: Department for Business, Enterprise and Regulatory Reform (BERR).
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