You are Here: Home >< Maths

# Product moment correlation Watch

1. If the table is like

Year: 1993 1994 1995
Consumption: 35.5 37.7 41.5

when I make the product moment correlation table, is x:
1993 1994 1995... etc

or 3 4 5 ? or something else?

because when I solve r, the numbers are so big because of the (year) dates and makes my Sxx negative so my result is wrong.
2. (Original post by 0utdoorz)
If the table is like

Year: 1993 1994 1995
Consumption: 35.5 37.7 41.5

when I make the product moment correlation table, is x:
1993 1994 1995... etc

or 3 4 5 ? or something else?
Either would do.

because when I solve r, the numbers are so big because of the (year) dates and makes my Sxx negative so my result is wrong.
Post working.
3. (Original post by ghostwalker)
Either would do.

Post working.
original table:

year: 1993 1994 1995 1996 1997 1998 1999 2000
consumption: 35.5 37.7 41.5 46.4 44.8 45.8 53.9 62

I did a product moment correlation table

x
1993
1994
1995
1996
1997
1998
1999
2000

y
35.5
37.7
41.5
46.4
44.8
45.8
53.9
62

x^2
3972049
3976036
3980025
3984016
3988009
3992004
3996001
4000000

y^2
1260.25
1421.29
1722.25
2152.96
2007.04
2097.64
2905.21
3844

xy
70751.5
75173.8
82792.5
92614.4
89465.6
91508.4
107746.1
124000

total x: 15972
total y: 367.6
total x^2: 31888140
total y^2: 17410.64
xy: 734052.3

sample x mean= 15972/8 = 1996.5
sample y mean = 367.6/8=45.95

sxx= 31888140-(8)(1996.5^2)= -28699958
syy= 17410.64-(8)(45.95^2)= 519.42

sxy = 734052.3-(8)(1996.5)(45.95)= 138.9

r= 138.9/ (sqrt(-28699958 * 519.42))

You can't sqrt a minus number!
4. When calculating Sxx and Syy, its dividing by 8, not multiplying...

sxx= 31888140-(1/8)(1996.5^2)= ???
syy= 17410.64-(1/8)(45.95^2)= ???

5. (Original post by Dalilsp)
When calculating Sxx and Syy, its dividing by 8, not multiplying...

sxx= 31888140-(1/8)(1996.5^2)= ???
syy= 17410.64-(1/8)(45.95^2)= ???

ooh how comes it's not 8?
I thought sxx was Ex^2 - (number of values) * sample mean x??
6. Sxx = E(X^2) - E(X)^2/n

Sorry I don't know how to use the fancy writing :P

Sxx = basically E(X^2) - (mean)^2
7. I did:

sxx= 3188140 - (1/8)*(1996.5)^2 = -179411.5313

syy= 17410.64-(1/8)*(45.95)^2=1476.714688

sxy= 734052.3-(1/8)(1996.5)(45.95)= 722584.9031

I still can't find r as sxx is negative so I can't square root it in the product moment correlation coefficient formula

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: April 18, 2013
Today on TSR

Can you relate?

### My alarm went off in an exam!

Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE