WJEC Maths for AS: Applied sample

2 Data presentation and interpretation 28 Strong and weak correlation Strong correlation is shown by points that lie close to a straight line. Strong positive correlation × × × × × × × × 0 x y Strong negative correlation × × × × × × 0 x y Weak correlation is shown by points that do not lie close to a straight line. Weak positive correlation × × × × × × 0 x y × × Weak negative correlation × × × × × × × × 0 x y × × Regression lines When two quantities are plotted against each other to produce a scatter graph and it is clear that there is a linear relationship between the variables then a line of best ϐit can be drawn. The straight line models the relationship between the two variables. If the two variables are x and y , then the line of best fit will have an equation of the form y = mx + c where m is the gradient of the line and c is where the line cuts the y -axis. Once the equation of the line has been found it can be used to ϐind a value of y that corresponds to a certain value of x and vice versa. Example 1 The table shows the temperature ( x ) and the number of visitors ( y ) at a beach. Temperature ( x ) °C 5 10 15 20 25 30 35 Visitor numbers ( y ) 17 30 40 53 60 85 90 (a) Present the data shown in the table as a scatter diagram. (b) Draw in the line of best ϐit.