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