The relationship between two continuous variables

Do you think that there is a relationship between women's heights and their weights? If you said yes, congratulations, you're right!

We can verify this assertion by using the data in R's built-in dataset, women, which holds the height and weight of 15 American women from ages 30 to 39.

  > head(women)
    height weight
  1     58    115
  2     59    117
  3     60    120
  4     61    123
  5     62    126
  6     63    129
  > nrow(women)
  [1] 15

Specifically, this relationship is referred to as a positive relationship, because as one of the variable increases, we expect an increase in the other variable.

The most typical visual representation of the relationship between two continuous variables is a scatterplot.

A scatterplot is displayed as a group of points whose position along the x-axis is established by one variable, and the position along the y-axis is established by the other. When there is a positive relationship, the dots, for...