Experimental and Correlational Research Study Guide

Experimental &
Correlational Research
Important Concepts you should be familiar with


Correlation =/ causation

Correlation: Is there an association between two variables?
Assume association  two variables changing together

Causality: is there an effect?
One happens  the other happens after

Must happen for causality to be in place:
1. Covariance: variables have an association
2. Directionality: cause precedes effect (in time)
3. Internal validity: eliminate alternative explanations

Scatterplots

Direction: positive vs. negative
Strength: more points clustered around one (straight) line = stronger relationship
Shape: linear vs. nonlinear / homogenous vs. heterogeneous

(if non-linear + heterogeneous = cannot measure correlation)

Covariance (sxy): measure the degree to which two variables vary together




Provides info:

Direction & Strength:

If near -1 and 1 = stronger relationship

If 0 = no relationship

If close to 0 = weak relationship

Disadvantage: The range of the covariance is dependent on the unit of measurement of the
variables