Question

Find the correlation coefficient of the line of best fit for the points (-3,-40), (1,12), (5,72), (7,137). Explain how you guy your answer. Use the coefficient to describe the correlation of this data.​

Answer 1

Answer:

r = 0.9825; good correlation.

Step-by-step explanation:

One formula for the correlation coefficient is  

$r = \dfrac{n\sum{xy} - \sum{x} \sum{y}}{\sqrt{n\left [\sum{x}^{2}-\left (\sum{x}\right )^{2}\right]\left [\sum{y}^{2}-\left (\sum{y}\right )^{2}\right]}}$

The calculation is not difficult, but it is tedious.

1. Calculate the intermediate numbers

We can display them in a table.

      x      y    xy   x²       y²  

      -3   -40    120     9     1600

       1      12      12      1        144

       5    72   360   25      5184

       7   137   959   49    18769

Σ = 10   181  1451   84   25697

2. Calculate the correlation coefficient

$r = \dfrac{n\sum{xy} - \sum{x} \sum{y}}{\sqrt{\left [n\sum{x}^{2}-\left (\sum{x}\right )^{2}\right]\left [n\sum{y}^{2}-\left (\sum{y}\right )^{2}\right]}}\\\\= \dfrac{4\times 1451 - 10\times 181}{\sqrt{[4\times 84 - 10^{2}][4\times25697 - 181^{2}]}}\\\\= \dfrac{5804 - 1810}{\sqrt{[336 - 100][102788 - 32761]}}\\\\= \dfrac{3994}{\sqrt{236\times70027}}\\\\= \dfrac{3994}{\sqrt{16526372}}\\\\= \dfrac{3994}{4065}\\\\= \mathbf{0.9825}$

The closer the value of r is to +1 or -1, the better the correlation is. The values of x and y are highly correlated.