Correlation

Question 1

What is a correlation?

Answer 1

An association between two co-variables.

Correlation refers to a mathematical technique which measures the relationship or association between two continuous variables (co-variables).

These are plotted on a Scattergram where each axis represents one of the variables being investigated

Question 2

Correlation Coefficient

Answer 2

Represents the strength of the correlation.

Statistical tests of correlation produce a numerical value somewhere between -1 and +1.
This the correlation co-efficient.
This value tells us the strength of the relationship between the two variables

Question 3

Strength of the Correlation Coefficient

Answer 3

The closer the coefficient is to 1 (+1 or -1), the stronger the relationship between the co-variables.

The closer to zero, the weaker the relationship is

However, it should be noted that coefficients that appear to indicate weak correlations (eg .30) can still statistically significant- it depends on the size of the data set

Question 4

The Direction of the Correlation

Answer 4

Correlation coefficient represents the direction of the correlation.
(note that a correlation coefficient of +.50 is as strong as -.50)

Question 5

The Value of +1

Answer 5

Represents a perfect positive correlation

Question 6

The Value of -1

Answer 6

Represents a perfect negative correlation

Question 7

What does the sign inform us of?

Answer 7

The direction of the correlation

Question 8

How are correlation coefficients calculated?

Give two examples?

Answer 8

Using an inferential test.

eg Pearson’s level (for interval level data) or Spearman’s