PSY 511: Correlation

Correlation Research

• Correlation looks at how two variables move together.
• It tells us if they are related, but not if one causes the other.
• The correlation coefficient is called r.

r in Correlation

The number of r (from 0 to 1 in absolute value) tells us how strong the relationship is.
• The sign of r
+ = positive

• - = negative

Graphing Correlation

• use scatterplot

How Strong or Weak Correlation is:

• Strong relationship 0. 70 to 1.00
• Moderate relationship 0.30 to 0.69
• Weak or almost no relationship 0.00 to 0. 29

Direction of Correlation

This tells us how the two variables move together.

• Positive (r>0) ↗

• Negative (r<0) ↘

• No Relationship

• Curvilinear  (curved shape)

r2

Tells you how much of the change in one variable can be explained by the other variable

Rules for Pearsons Correlation

• interval or ratio scale

• assumes your data is linearly related

• assumes homoscedasticity in the data

• assumes we do not have restricted range