Super Size Me
• Critiques: three times a day was overkill, McDonald’s does not have variety, he
decreased exercise in addition to eating poorly, he ate way more than he was previously
• Can we get conclusions?
o Just one person/example
o We don’t have any kind of control
• To what extent does the independent variable account for differences in the dependent
• Control: what means are needed to ensure this?
Threats to Internal Validity
• History: events that occur outside the study that are experienced by participants and
could influence results
• Maturation: changes in each individual due to naturally occurring processes
o Ex. measuring the success of therapy; most depression naturally decreases over
time—you can’t conclude that it was entirely due to therapy
o Older, stronger, wiser, more tired, more bored, any change over time
• Testing: performance influenced by taking tests re