Normalization

Correaltion

A correlation is a single number that describes the degree of relationship between two variables.


Correlation Example

This is an example showing how to find the relationship between height and self esteem.

Person	Height	Self Esteem
1	68	4.1
2	71	4.6
3	62	3.8
4	75	4.4
5	58	3.2
6	60	3.1
7	67	3.8
8	68	4.1
9	71	4.3
10	69	3.7
11	68	3.5
12	67	3.2
13	63	3.7
14	62	3.3
15	60	3.4
16	63	4.0
17	65	4.1
18	67	3.8
19	63	3.4
20	61	3.6

 

 

We can see that the relationship between the variables is a positive one. A positive relationship means that higher score on one variable tend to be paired with higher scores on the other.

Calculating the Correlation

The above is a graphical method to show the relationship. Actually, there is a method to compute a value to represent the relationship, that is correlation coefficient.

 

 We user the symbol r to stand for the correlation. Through the magic of mathematics, it turns out that r will always be between -1.0 and +1.0.If the correlation is negative, we have a negative relationship.

The correlation Matrix

In most studies, we have considerably more than two variables.




From: http://www.socialresearchmethods.net/kb/statcorr.php