SCATTERPLOT Decide whether or not a relationship exists between the variables and, if it does, comment on whether it is positive or negative; weak, moderate or strong: and whether or not it has a linear form
EXAMPLE Data showing the average weekly number of hours studied by each student in year 12 at Strathmore Secondary College and the corresponding height of each student.
There is a formula, but r is often done using CAS calculator. There are two limitations when using r: 1. Since r measures the strength of a linear relationship, it would be inappropriate to calculate r for data which are not linear. 2. Outliers can bias the value of r. Therefore, it will make it an unreliable measure of the strength of that linear relationship. CALCULATING R AND THE COEFFICIENT OF DETERMINATION WE MUST DRAW A SCATTERPLOT FIRST IN ORDER TO CHECK FOR A LINEAR FORM BEFORE r IS CALCULATED