correlation. Are two variables related?. 1. Do they move together or opposite ?. 2. How strongly?. (if they are strongly related, we can predict one from the other). correlation coefficient. NO ASSN. NEGATIVE. POSITIVE. 1.00 0 +1.00.
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correlation
Are two variables related?
1. Do they move together or opposite?
2. How strongly?
(if they are strongly related, we can predict one from the other)
correlation coefficient
NO ASSN
NEGATIVE
POSITIVE
1.00 0 +1.00
= direction
+ / 
number
= strength
sign (+ or )
move together or opposite?
positive
correlation
+
negative
correlation

positive correlation
Variable 1
Variable 2
# of shoes you own
amt of credit card debt
move together, in same direction
correlational studies
POSITIVE
NEGATIVE
NO ASSN
Are shy people happy?
To a group of people, give a questionnaire about their degree of shyness.
To this same group, give a questionnaire about their degree of happiness.
Each person has two scores. Use correlation.
Is there a relationship between shyness & happiness? (Did one cause the other?)
correlational studies
Correlation is NOT causation!
B
A
B
A
A
C
B
example
Variable 1
Variable 2
ice cream sales
violent crime
Ice cream sales positively correlate with the occurrence of violent crime.
e.g.
example
Variable 1
Variable 2
# parties at your house
# of friends linked at Facebook
# parties at your house positively correlate with # of friends linked at Facebook
e.g.
correlation coefficient
NO ASSN
NEGATIVE
POSITIVE
1.00 0 +1.00
= direction
+ / 
= strength
number
weak (0  .40)
moderate (.41  .69)
strong (.70 – 1.00)
correlation coefficient
NO ASSN
NEGATIVE
POSITIVE
1.00 0 +1.00
= direction
+ / 
= strength
number
correlation coefficient
NO ASSN
NEGATIVE
POSITIVE
1.00 0 +1.00
= direction
+ / 
= strength
number
real examples
Variable 1
Variable 2
+.90
height of twin #1
height of twin #2
+.50
marriage problems
behavioral problems in children
+.45
height of sister #1
height of sister #2
+.20
exposure to violent media
reallife violent behavior
.40
amt of social support
frequency of illness
experimental research
Hypothesis:
Systematic desensitization therapy eliminates phobias.
DEPENDENT VARIABLE
INDEPENDENT
VARIABLE