# Correlation

Correlation statistics

- Created by: Rukiya Majid
- Created on: 13-05-09 14:23

First 225 words of the document:

S1 Revision Notes: Correlation

Section 1: Productmoment correlation coefficient

Recap:

The productmoment correlation coefficient, r, measures how close the points on a scatter graph lie to a

straight line (or more mathematically it measures the strength of the linear relationship between two

variables).

The key points:

r always lies between 1 and 1. (If you calculate a value of r that does not lie between 1 and 1 then

you've made a mistake!!).

The formula for calculating r is

,

where

.

Note: These formulae are in the formula book.

Normally you can use your calculator's r button for finding a correlation coefficient see later.

Example:

In a school there are 10 students on the first year of an Alevel Geography course who also study

mathematics at Alevel. The table shows the marks of each student in the mock examinations in

Geography and Mathematics.

Student Geography mark, x Maths mark, y

A 79 63

B 72 58

C 57 78

D 78 80

E 73 75

F 56 63

G 83 77

H 81 92

I 13 11

J 62 90

a) Calculate the value of the productmoment correlation coefficient between x and y and interpret the

value that you obtain.

b) Plot a scatter graph of these data.

1

Created on 13/05/2005 10:18 AM by A. Duncombe

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