1. Evaluating research
Is this valid research?

2. Internal Validity
The extent to which a study establishes a cause and effect relationship between two variables
Internal validity asks:
Are there any alternative explanations for this finding? • Do the researchers rule-out plausible alternative explanations?

3. Establishing Internal Validity
True Independent Variables
Assignment Bias
Random Assignment vs. Matching

4. Assignment Bias
Occurs when the process used to assign different participants to different treatments produce groups of individuals with noticeably different characteristics

5. Matching CD 1 CD 2 CD 1 CD 2 NOT Matched Variables Matched Variable MF
CD 1
CD 2 M F

6. Random Assignment
Participants have an equal chance of being in any condition in the experiment

7. Establishing Internal Validity
True Independent Variables
Assignment Bias
Random Assignment vs. Matching
Experimental Control
Ruling out alternative Explanations
Replication (for internal validity goals)

8. Establishing Internal Validity
True Independent Variables
Assignment Bias
Random Assignment vs. Matching
Experimental Control
Ruling out alternative Explanations
Replication (for internal validity goals)
Manipulation Checks
Establishing the manipulation worked