Quasi-Experiments Study Notes

Quasi-Experiments

Definition

  • A quasi-experiment is a type of research design that lacks random assignment of participants to conditions or groups.
  • Quasi-experiments are characterized by the presence of an independent variable (IV) that is not manipulated by the researcher but is instead naturally occurring.

Main Features of Quasi-Experiments

  • Two main features define quasi-experiments:
    • Natural Independent Variable: The independent variable is not manipulated; it varies naturally.
    • Difference Studies: These studies do not have a true independent variable as they are based on existing differences between groups.

Types of Quasi-Experiments

  1. Natural Experiments:

    • Conducted when it is not feasible to manipulate an IV for ethical or practical reasons.
    • The IV in natural experiments occurs naturally.
    • Example:
      • Berkowitz (1970):
      • Analyzed monthly FBI crime statistics from January 1960 to December 1966.
      • Found a significant rise in violent crimes post-November 1963, attributing it to the exposure of the American public to the assassination footage of John F. Kennedy.
      • IV: Exposure to assassination footage.
    • Example:
      • Charlton et al. (2000):
      • Studied the impact of the introduction of television on the small island of St Helena before 1995.
      • Found no significant changes in pro- or anti-social behavior post-introduction of TV.
      • IV: The presence of TV.

  2. Difference Studies:

    • The apparent IV exists naturally between groups (e.g., gender, age).
    • The DV may still be measured in a controlled environment like a laboratory.
    • Example:
      • Sheridan and King (1972):
      • Examined obedience by assessing male and female participants in giving electric shocks to a puppy.
      • Found that 54% of males delivered the maximum shock, while 100% of females did.
      • IV: Gender (not manipulated).
    • Example:
      • Rosenbluth et al. (2000):
      • Compared olfactory abilities between non-sighted and sighted children.
      • Matched 30 non-sighted children with 30 sighted in terms of age, sex, and ethnicity.
      • Found non-sighted children scored higher on olfactory tasks: 12.1 vs 10.4 (sighted).
      • IV: Visual ability (sighted vs non-sighted).

Applications in Psychology

  • Many psychological studies utilize quasi-experiments to examine behaviors across different conditions such as age or gender.
  • For instance, studies comparing eyewitness testimony accuracy often use age as an IV. This characteristic of individuals is a deterministic condition, thus qualifying as a quasi-experiment.