Chapter 1

Psychological Science

Correlational Research

Correlation A statement of Relationship between two

variables. One variable usually predicts the other.Does ACT score predict future college

success?Does a high stress work environment predict

chances of heart disease?Does the education level of your parents

predict whether or not you will drink?

Correlation Correlations can be positive or negative.

Positive correlation: As one variable increases or decreases, so does the other.

Increased smoking, increased risk of lung cancer The less you study, the lower your grade

Negative correlation: As one variable moves, the other moves in the opposite direction.

As exercise increases, chance of sickness decreases As self-esteem rises, depression levels decrease

Correlation Correlation Coefficient

a statistical measure of the extent to which two factors vary together, and thus how well either factor predicts the other

Correlation coefficient

Indicates directionof relationship

(positive or negative)

Indicates strengthof relationship(0.00 to 1.00)

r = +.37

Correlation

Scatterplot a graphed cluster of dots, each of which

represents the values of two variables the slope of the points suggests the direction of

the relationship the amount of scatter suggests the strength of

the correlation little scatter indicates high correlation

also called a scattergram or scatter diagram

Correlation

Perfect positivecorrelation (+1.00)

No relationship (0.00) Perfect negativecorrelation (-1.00)

Scatterplots, showing patterns of correlations

CorrelationHeight and Temperament of 20 Men

12345678910

11121314151617181920

80636179746962757760

64767166737063716870

75666090604242608139

48697257637530578439

SubjectHeight in

Inches Temperament SubjectHeight in

Inches Temperament

Correlation

Scatterplot of Height and Temperament

55 60 65 70 75 80 85

959085807570656055504540353025

Temperamentscores

Height in inches

Correlation and Causation

It has been found that people with low self-esteem have a higher rate of depression than people with high self-esteem.

Does low self-esteem cause depression?

Correlation and Causation

Three Possible Cause-Effect Relationships(1)

Low self-esteemDepression

(2)Depression

Low self-esteem

Low self-esteem

Depression

(3)Distressing events

or biologicalpredisposition

could cause

could cause

could cause

or

or

and

Correlation and Causation Third Factor error

An unknown variable may be causing changes in both variables in question

Directional errorThe inability to determine which variable is the

cause and which is the result

Illusory Correlation

Illusory Correlation A belief that there is a relationship where none

actually exists

A result of confirmation bias

Examples: Superstitions?

Two Hands Dealt in Poker

Two series of coin flips

T-H-H-T-H-T-T-H-T-H

T-T-T-T-T-T-T-T-T-T

Perceiving Order in Random Events Your chances of being dealt either of

these hands is precisely the same: 1 in 2,598,960.

The chances of each series of coin flips is exactly the same because the chances of heads or tails on any one flip is 50%

Perceiving Order in Random Events The chances of a statistically improbable

event happening to you is incredibly unlikely.

That it should happen to someone at sometime is very likely.

Consider This: An event happening to someone that has a 1 in a billion chance of happening, happens six times a day, every day.