Defining new variables
When given a data set to analyse, think about whether its variables are the most useful ones to analyse. Sometimes a simple transformation provides a variable whose values are more meaningful or highlight a different aspect of the data.
For example, it is usually more meaningful to compare the population density of countries than either their populations or areas:
Density = | Population | × 1000 |
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Area |
As another example, although it is interesting to compare the calorie intake of countries, it is also appropriate to look at their percentage change over different periods:
%Increase = 100 × | 2009 calories − 2004 calories |
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2004 calories |