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Correlation Research

Goal is to explore ______________ between variables

Causal-comparative research: compare mean scores across groups. The “IV” is a __________ variable.

e.g., compare salaries in those who complete and do not complete college

Correlational research: analyze multiple scores ______ _____________. Collect two sets of data for each participant at one point in time. The “IV” is a quantitative variable.

e.g., compare number of years of education to salary

Neither approach yields ____________ information

Both are non-experimental – no manipulation of an ___

Both used when researchers are _________ to experiment

GRP 1 GRP 2

Causal-Comparative

1 measure

Meas. 1

Correlational

Meas. 2

1 group

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2 Types of Variables

______________ variables (~IV) allow prediction of some criterion variables

e.g., SAT & college GPA e.g., TV & aggression

_____________ variables (~DV) the object of our research

e.g., SAT & college GPA e.g., TV & aggression

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Method

Develop hypothesis or research question e.g., What is the relationship between x and y?

Select homogenous group Data collection

measures must be psychometrically sound Data analysis

correlational statistics (______________) - denotes strength of correlation, sign +/- indicates direction

Graphed on a ______________ Correlation coefficients range from ___________

Threats to Internal validity no huge concerns- not identifying functional relationship

Threats to External validity _______________________ of sample

Positive correlationAs one variable goes up, the other variable goes

___, e.g., class attendance and grades

Negative correlationAs one variable goes up, the other goes _____,

e.g., alcohol consumption and grades

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Factors Affecting Coefficients

1. ___________________ a curvilinear relationship would result in a lower

coefficient Correlation-coefficients only useful for linear

relationships2. Outliers

_____________ scores May inflate or deflate r values

3. Restricted ___________ Reduces correlation e.g., GPA & SAT

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Non-linear relationships

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0 20 40 60 80

Energy Level/Arousal

Task P

erf

orm

an

ce

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0 20 40 60 80

Task Complexity

Str

ess

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Outliers

0123456789

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0 1 2 3 4 5

X

Y

0

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Range restriction

0

0.5

11.5

2

2.5

33.5

4

4.5

400 600 800 1000 1200 1400 1600

SAT

Co

lleg

e G

PA

22.22.42.62.8

33.23.43.63.8

4

1100 1200 1300 1400 1500 1600

SAT

Co

lleg

e G

PA

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Correlation vs. Causation If no correlational relationship, no causation Strong relationship might suggest a causal relationship, but A strong relationship could also be the result of:

1. A ____________ (chance) relationshipe.g., tobacco industry states no direct causal link between smoking

and lung cancer in humans, only correlational data

2. _________________ - A causes B, or B causes Ae.g. Violent TV and children’s aggression

3. ______________ - anther variable influences both A and Be.g., Aggressive parents or social skills may influence both preference

for violent TV and aggressive behavior

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Describe some problems of determining causality.

Amount of soda consumed each day is correlated with obesity level

Height of children is correlated with popularity Number of hours of sleep per night is

correlated with depression

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Problem with correlations: The Case Against Bread

More than 98% of convicted felons are bread users. Fully half of all children who grow up in bread consuming

households score below average on standardized tests.

In the 18th century, when virtually all bread was baked in the home, the average life expectancy was less than 50 years; infant mortality rates were unacceptably high; many women died in childbirth; and diseases such as typhoid, yellow fever, and influenza ravaged whole nations.

More than 90% of all violent crimes are committed within 24 hours of eating bread.

Primitive tribal societies that have no bread exhibit a low incidence of cancer, Alzheimer's, and Parkinson's disease.

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Research Design:

You are interested in the relationship between exercise and stress. How would you design a study to investigate this relationship using:

A causal comparative design?

A correlational study?

Why would you choose one over the other?

Helping determine causality:_____________________correlation Measures two variables at two points in time

B at Time 1 correlated with A atTime 2. Supports view that B affects A

A at Time 1 correlated with B atTime 2. Supports view that A affects B

A A

B B

.30 .25

.01

.32

.25

.03

Time 1 Time 2

A A

B B

.30 .25

.35

.05

.25

.03

Time 1 Time 2

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Allows you to help rule out a _____ variable as a cause. Relationship between stress and alcohol

consumption – also measure socioeconomic status to control or “__________” the influence of a third variable.

Helping determine causality:Partial-correlations

A B

C.43 .52

.32.02

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_______________ correlation - Correlation between two variables e.g., relation between stress and alcohol consumption

_________________ correlation - Correlation between multiple predictor and one criterion variables e.g., relation between stress, socio-economic status,

family history and alcohol consumption Also allows you to rule out or analyze the effects of

many third variables

Helping determine causality:Multivariate-correlations