1. Even Muppets can do correlations! AQA Spec 3.2.3

2. Hello ! I am fozzy bear and we are going to look at facebook today
fozzy on facebook
Hello !
I am fozzy bear and we are going to look at facebook today
Yay !!!

3. It’s all about friends – right ?
OK – so here is my Facebook page and lets all agree about one thing;
Facebook is all about friends – right ?
The more friends you have – the happier you will be :o)

4. It’s all about friends – right ?
That means there is a positive correlation between friends and happiness.
A correlation is a relationship between two variables where changes in one variable go along with changes in the other variable.
So back to facebook: the more friends you have – the happier you will be :o)

5. There are 2 types of correlations
Positive
Negative
Variable Y
Variable Y
Variable X
Variable X

6. Positive Correlations
The variables change in the same direction,
Like friends and happiness.
Number of Friends
Happiness

7. Negative Correlations
The variables change in opposite directions
As friends increase, loneliness will decrease.
Number of Friends
Loneliness

8. The Coefficient of Correlation
If you were reporting your research you couldn’t just say “the line slopes up to the right a bit” or “it looks positive”
There is a mathematical value for any correlation.
We call this the coefficient of the correlation.
This as a mathematical phenomenon

9. A coefficient of 0.00 means there is no relationship between the variables.
If we compared the number of friends people have to the % mark they got in their year 7 French exam, we might find there was just no connection.
Sally got 70% and Billy got 30% but they both have 120 friends
This is a zero folks !

10. The Coefficient of Correlation
A value of means a perfect, positive correlation.
The more hours you work – the more money you get.
If there is a 100% correspondence between the two, then the correlation would be +1.00
[We all know one whole one is 100% right ?]

11. The Coefficient of Correlation
A value of means a perfect, negative correlation.
The more money you spend – the less you have in the bank.
There could be a 100% negative correlation between spending and saving.

12. In the real world you don’t often find perfect correlations, usually they are weaker.
If I say there is a +0.4 correlation between the number of friends people have on Facebook and the number they have in real life.
How could that be?

13. In the real world you don’t often find perfect correlations, usually they are weaker.
If there was a – 0.7 correlation between the time spent on facebook and the time spent on homework – why is it not ?

14. Useful for the exam
3 advantages of correlations:
2 disadvantages
They may indicate a connection between 2 issues in situations where experimental proof is impossible.
They do not require manipulation of variables and are therefore safer and more ethical than doing experiments on humans.
High ecological validity – these numbers came from real life
They do not prove a causal relationship.

15. Problems with Correlations (1)
Correlations show linear relationships but do not reflect curvilinear ones – so for example the effect of stress on exam performance :
But really it’s a curve
Correlation shows it as a straight line.
Exam Mark
Exam Mark
Stress
Stress

16. Problems with Correlations (2)
Correlations demonstrate that there may be a relationship between two sets of data.
But they don’t show what the cause is !!!
You have to try to work out the relationship.
Don’t fall for the trap of thinking that one aspect automatically causes the other.
Suppose I find a correlation between shoe size and the number of facebook friends ?
Does that mean that one of them causes the other?
I don’t think so :o)

17. The “third variable” problem
Does violent crime make people buy more ice-cream?
Does eating ice-cream cause violent crime ?
Or is there a “Third Variable” which is causing both ?
Ice cream sales
Violent crime
Oh my ! Oh my ! What could that third variable be?

18. Why not causation? A B B A A C B X A Y B Maybe A causes B
Or maybe B causes A
But something else might cause both.
Or the two things might not be related at all B A C B A X A Y B

19. Does facebook improve A Level grades?
Maybe increased use of facebook is pushing up grades
Or maybe better educated students use facebook more
But maybe more access to computers has improved A level grades AND led to more people using facebook.
Or the two things might not be related at all.
More online access has boosted facebook
Better teaching pushes up grades. A B B A C B A C A D B

20. Class Activity
Do a simple scatter graph and correlation line on the whiteboard using these two items of data:
Like fitness level and number of hours a week spent exercising
Or number of calories eaten a day and weight
Or temperature and ice cream sales
Is your correlation positive or negative ?
Now come up with an example of the opposite

21. Studies you know.
What type of correlation did Bahrick find between the years which had passed and the number of pictures recognised?
Belskey found that children who spent too many hours per week in nursery care were more aggressive later – what kind of correlation is that ?
Which two measurements were correlated by the Petersons in their famous experiment.

22. Classwork questions
If teenagers have more facebook friends than old people does that prove they are more friendly?
Is the correlation between time spent on facebook and % marks in exams likely to be positive or negative.

23. Slightly more difficult
If we found a strong positive correlation between high levels of aggression and the hormone testosterone, which would be the independent variable.
In scientific terms, what is wrong with this sentence:
“Research has found a correlation level of 64.7 between watching violent movies and committing crimes, proving once and for all that such films damage children.”

24. Written Activities
What are the advantages and disadvantages of correlations (from GHG page and Oxf page 22-25)
Imagine doing a correlation between age, and how many friends people have on facebook.
What disadvantage with correlations might that illustrate?

25. Once you are confident with correlations…
It’s time to ensure you understand other types of graphs. Using GHG p or Oxf p55-61 Write a sentence about each type of graph and when you would use it .

26. Can you recognise when data is skewed?

27. Teachers Only Here are the answers to the questions.
Bahrick – negative correlation
Belskey – positive
Petersons - Time, and frequency of remembering trigram
Teenagers v old people = correlations don't prove causes
Negative correlation more likely between time on facebook and exam marks
No independent variable in a correlation – if there was it would be an experiment
Correlations cannot be more than AND they don't prove anything – they only demonstrate a link.
Correlating age and friends on facebook – would fail to allow for the curve – just like the example on stress