Measures of relationships between variables

So far, we have been reviewing univariate measures, as in the data sets that have just one variable - heights, weights, lengths, etc. It's time we explored data sets with more than one variable in them and measure the relationships among these variables.

For example, the temperature and sales of ice cream at a store. As you would expect, the higher the temperature, the higher the sales of ice creams. But does that always happen? Could we collect data to prove it? Would the data throw up something unexpected?

These are questions we will explore as we go through the following topics:

• Covariance
• Correlation