3. Natural and Quasi experiments

• A quasi experiment is an experimental design that does not have random assignment to conditions.
• The main problem with quasi-experimental designs is the lack of control over extraneous variables which can lead to confounding effects
• The main difference between true experiments and quasi-experiments is the lack of random assignment to conditions in quasi-experiments.
• a true experiment aims to establish a cause and effect relationship between an IV and DV by controlling all other factors.
• natural-

  The IV is naturally occurring. The researcher does not directly change it.
• Quasi-


  The IV is a characteristic of the participants and so no under the researchers control (e.g age, gender, IQ)
• Natural experiments are when the researcher takes advantage of a naturally occurring independent variable. It is called natural because the variable would have changed even if the experimenter was not interested (eg charlton).
• A weakness of using a natural experiment is that there may be many uncontrolled variables present making it difficult to determine whether any observed differences were caused by the IV or another factor.
• Quasi experiments have an IV that is based on an existing difference (innate) between people (age/gender). The key feature is that the IV is a characteristic of the participants and therefore not under the researchers control and cannot be changed.
• What is a key characteristic of quasi-experiments regarding participant assignment?


  Participants are assigned to groups based on pre-existing conditions.
• Why does the lack of random assignment in quasi-experiments make it harder to rule out other factors?


  Because participants are grouped based on characteristics that may influence the outcome.
• What do quasi-experiments manipulate and measure?


  They manipulate an independent variable (IV) and measure its effect on a dependent variable (DV).
• What is an example of an independent variable (IV) in a quasi-experiment?


  A treatment or intervention.
• What is an example of a dependent variable (DV) in a quasi-experiment?


  Test scores.
• How does the presence of a control group in quasi-experiments affect internal validity?


  It may not be randomly selected, which can compromise internal validity.
• What are the key characteristics of quasi-experiments?


  • No random assignment of participants
  • Manipulation of an independent variable (IV)
  • Measurement of a dependent variable (DV)
  • Control group may or may not be present, typically not randomly selected