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
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
