AP PSYCH 1.3 Defining Psychological Science: The Experimental Method

• Experiments are the only way to find a causal relationship
• One factor, the independent variable, causes a change in something else, the dependent factor

Hypothesis

• A prediction
  • An if/then statement
• If we manipulate the independent variable and everything else is constant, then the dependent variable will change because of the independent variables’ effect
• Holding everything else constant, so that there are no other factors changing the outcome, is called experimental control

Independent Variable

• Not everyone/everything receives the independent variable
• If everything is treated, how can you tell if it is working, and to what degree?
• Keeping a control that receives no treatment and knows they aren’t is important to compare
• It is also important to have a group who does not receive the independent variable but thinks they did
  • This can result in placebo, where participants report an effect believing it due to the independent variable
  • This determines how much of the treatment is psychological and how much is actual affects
• Other unintentional factors that may affect the dependent variable are called confounding factors
• For the best and most accurate data, participants should be randomly assigned to groups

Three Terms

• These three terms are often confused with one another

Random Sample/Random Selection

• Each person in a large population has equal chance of being chosen for the study

Representative Sample

• The group “looks like,” represents, the larger population
• Means that findings may be generalizable

Random Assignment

• Each participant has an equal change of being put into the experimental or placebo group

Control vs. Confounding Variables

• As control increases, confounding variables decrease
• You could conduct an experiment in a heavily controlled environment, but people do not live in a lab
  • By putting them in an unnatural environment, you are introducing a confounding variable: the potential for them to act differently
  • This poses a unique challenge to getting good data

The Experimental Method

• All experiments have…
  • A hypothesis
  • Independent variable
  • Dependent variable
  • Experimental group
  • Control group
  • Placebo group
  • Placebo
  • Random assignment
• Without these factors, experiments would rise validity and might sacrifice the ability to prove casualty

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