*What Scale?
Throughout this unit you have been looking at illusions and experiments. Did you notice that you have had different types of answer? We say the answers are measured on different SCALES. In illusion 7 you were either right or wrong. When making a table of results, it does not matter which order you put these two answers in. Another example where order does not matter is in listing Pupils favourite sports. It would not matter if you put the answers in the order 'soccer, cricket, tennis' or 'tennis, soccer, 'cricket'. When the order does not matter, we have a NOMINAL scale. Since there is no correct order we can calculate a mode but not a median or a mean.

In illusion 6 there was a proper order. The lines were put in order of length. But the difference between lines EF and AB was not the same as that between AB and GH. The order was important, but the answers were not equaliv spaced. In this case we have an ORDINAL scale. With an ordinal scale we can find modes and medians, but not means.

When you did the experiments in C1, you measured your answers to the nearest 2 mm. The answers can be put in order of length, and every 2 mm interval is the same length. On the other hand, an answer of 0 mm did not mean that you had made no mistake. This is an example of an INTERVAL scale. With an interval scale we can find modes, medians and means.

In Section C6 you measured errors to the nearest 2 mm. The errors can be put in order of length. Every 2 mm is the same length, and an error of 0 mm means that there was no mistake. An error of 12 mm is twice the error of' 6 mm. These measurements are on a RATIO scale. With a ratio scale we can find modes, medians and means. We can also divide two answers to find how much bigger one is than the other.

Your teacher will explain this flow chart to you. It will help you to say which scale you are using.

Some of these statements must be wrong. Say which and give a reason:

For each of the following say whether you have a nominal, ordinal, interval or ratio scale:

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