Correlational Research

AP PsychologyMs. Desgrosellier

9.30.2009

Objectives SWBAT describe positive and negative

correlations, and explain how correlational research measures can aid the process of prediction.

SWBAT explain why correlational research fails to provide evidence of cause-effect relationships.

SWBAT describe how people form illusory correlations.

Correlation Describing behavior is the first step

toward predicting it. A correlation is measure of the extent to

which two factors vary together, and this how well either factor predicts the other.

Correlation coefficient is the mathematical expression of the relationship, ranging from -1 to +1.

Correlation Coefficient

r = +.037 r = correlation coefficient +/- = the direction of the

relationship (positive or negative) # = strength of the relationship

(.00 to 1.00)

Correlation Coefficient

Scatterplots A graphed cluster of dots, each

representing the values of two variables. The slope of the points suggests the

direction of the relationship between the variables. Bottom left to upper right = positive (as one

goes up, so does the other) Top left to bottom right = negative (as one

goes up, the other goes down) The amount of scatter suggests the

strength of the correlation. Little scatter = high correlation.

Scatterplots

Correlations

Example: Is there a correlation between height and age?

http://easycalculation.com/statistics/correlation.php

What do correlations tell us? They are informative, but they usually

leave most of the variation among individuals unpredicted.

Research shows that there is a relationship (correlation) between parents’ abusiveness and their children’s later abusiveness when they become parents.

Simply indicates a relationship: most abused children do not grow into abusers, non abused children are just less likely to become abusive.

Correlations

Bottom line: A correlation coefficient helps us see the world more clearly by revealing the extent to which two things relate.

Correlations and Causation: Can you say that a correlation means that

something caused something else to happen?

NO. Correlation ≠ Causation!!! For example, there is a positive correlation

between length of marriage and hair loss in men

Potential relationships: Hair loss causes longer marriages Longer marriages causes men to lose their hair OR age explains both (a third factor).

Correlations and Causation:

Bottom line: Correlation indicates the possibility of a cause-effect relationship, but it does not prove causation!

Illusory Correlations The perception of a relationship where

none exists. When we believe there is a relationship

between two things, we are likely to notice and recall instances that confirm our belief.

We also forget or ignore instances that disprove our belief

Bottom line: when we notice random coincidences, we may forget that they are random and instead see them as correlated. We can easily trick ourselves by seeing what is not there.

Illusory Correlations

Sick Not Sick

Cold/Wet

Confirming evidence Disconfirming evidence

Not Cold/Wet

Disconfirming evidence Confirming evidence

Shark attack! For example, a study published said that

there is a correlation between ice cream sales and shark attacks in Southern California.

Potential relationships: Shark attacks cause people to eat ice cream Eating ice cream causes sharks to attack you Third factor? They aren’t related at all!

Spurious relationship. What is the actual cause?

Shark attack!

Ice cream sales go up in the summer. There are also more people in the ocean, thus increasing the likelihood of a shark attack.