Correlation
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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.

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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

real-life violent behavior

-.40

amt of social support

frequency of illness


experimental research

Hypothesis:

Systematic desensitization therapy eliminates phobias.

DEPENDENT VARIABLE

INDEPENDENT

VARIABLE


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