Correlation Coefficient

Question 1

What does the correlation coefficient do?

Answer 1

Measures how strongly two variables are related and in what direction they are related.

Question 2

What is correlation coefficient denoted as?

Answer 2

r

Question 3

What values can r take?

Answer 3

Any value between -1 and +1.

Question 4

What does an r value of +1 mean?

Answer 4

+1 = a perfectly positive correlation (when one goes up the other one always goes up)
points lie exactly on the straight line

Question 5

What does an r value of -1 mean?

Answer 5

-1 = a perfectly negative correlation (when one goes up the other one always goes down)
points lie exactly on the straight line

Question 6

What does a value of r>0 mean?

Answer 6

A positive slope
The closer the number to 1 the stronger the relationship

Question 7

What does a value of r<0 mean?

Answer 7

A negative slope
The closer the number to -1 the stronger the relationship

Question 8

What does r=0 mean?

Answer 8

There is no linear relationship between the variables.

Question 9

When is correlation coefficient unsuitable?

Answer 9

Relationship is non-linear
Variables measured over more than 1 distinct group
One or more outliers with strong influence
Restricted sampling of individuals

Question 10

How do you calculate r?

Answer 10

r = covariance of X and Y divided by (SD of X) x (SD of Y)