Paired data

When two types measurements, X and Y, are made from each individual (or other unit), the data are called bivariate. Sometimes the two measurements are of closely related quantities, perhaps even describing the same quantity at different times.

When the sum or difference of X and Y is a meaningful quantity, the data are called paired data.

With paired data, we could investigate the relationship between the variables, but we are often more interested in whether the means of the two variables are the same.

We now describe a few scenarios that lead to paired data.

Pre-test, post-test data

Twin studies

Other paired data