1. Correlation

2. What is a correlation?
A correlation looks at the relationship between two variables.
There are 2 types of relationship-POSITIVE when one variable increases the other variable increases.
NEGATIVE-when one variable increases and the other decreases.
Correlations can be presented graphically on a SCATTERGRAPH.
Or presented statistically using the CORRELATION COEFFICIENT.

4. Positive or negative?
Identify whether the following are positive or negative correlations?
The more time a child spend in daycare the more aggressive they are.
The more time a child spends in daycare the more sociable a child is.
The more time a child spends in daycare the less they are attached to their mothers.
The more time a child spends in daycare the less talkative they are.
The more stressed a person is the more colds they have.
The more stressed a person is the more time off sick they have.
The more securely attached a child is the more friends they have.
The more stressed a person is the lower their blood pressure.
The more you brush your teeth the less fillings you have.
The more sweets you eat the more fillings you have.
The more parents smack, the more aggressive the child.
The more parents read to their children the better the child is at talking.

5. The correlation coefficient
The closer the correlation coefficient is to one the stronger the correlation.
A PERFECT CORRELATION = 1
A STRONG correlation is or 0.8 or 0.9
A MODERATE correlation is 0.4 or 0.5 or 0.6
A WEAK correlation of is 0.1 or 0.2 or 0.3
No CORRELATION=0

6. Do this activity Strong , moderate or weak correlation?
0.6________________________________
0.9________________________________
0.77_______________________________
0.5________________________________
0.4________________________________
0.88_______________________________
0.3________________________________

7. PUTTING IT TOGETHER;
The SIGN (+ or -) tells you the DIRECTION of the correlation (positive or negative).
If the correlation is negative, there is a minus sign.
The NUMBER tells you if the correlation is STRONG , MODERATE, or WEAK
Describe the following correlations;
+0.8 ____________________________________________
+0.4 ___________________________________________
+0.1____________________________________________
-0.9_____________________________________________
-0.3 ____________________________________________
-0.8 ____________________________________________

8. Strengths of Correlations
Correlations are useful when it would not be practical or ethical to do an experiment-because the variables cannot be manipulated.

9. Correlations allow us to make predictions
Correlations allow us to make predictions. Once we have established a correlation- if we know variable X we can predict variable Y. e.g…

10. Use variable X to predict variable Y

11. Strengths of correlation:
Good preliminary tool for research: suggest ideas for future resrach.
Quick and economical to carry out.
Data collected by others can be used, so less time consuming.

12. Weaknesses of correlation
Correlations cannot show causation.
People often MISINTERPRET correlations and think if two variables are related one must CAUSE the other-however we cannot say this-because extraneous variables have NOT been held constant- there could be a third unknown variable influencing the results.

13. e.g there is a positive correlation between ice-cream sales and aggression rates (the more ice-creams are sold the more acts of aggression are committed).
Does ice-cream cause aggression?

14. No. There is a third variable-heat
No. There is a third variable-heat. People are more aggressive when it is hot, and people also buy more ice-cream when its hot!

15. Activity
Drawing scattergraphs
Interpreting scattergraphs