Experimentation Basics

• Experimental psychology


  An undergraduate psychology course designed to provide students with knowledge about and hands-on practice with experimental research methods in psychology
• Experiment


  • A type of study designed specifically to answer the question of whether there is a causal relationship between two variables
  • The researcher manipulates, or systematically varies, the level of the independent variable
  • The researcher controls, or minimizes the variability in, variables other than the independent and dependent variable
• Hypothesis

  A very specific testable statement that can be evaluated from observable data
• Testable hypotheses


  • Students who attend class have higher grades than students who skip class
  • People exposed to high levels of ultraviolet light have a higher incidence of cancer than the norm
• Hypothesis

  • Must be synthetic, testable, falsifiable, parsimonious, and (hopefully) fruitful
• Dependent variable


  • Should be stable, with a wide enough range to avoid floor or ceiling effects
• Reliability

  The consistency of experimental operational definitions and measured operational definitions
• Types of reliability

  • Interrater reliability
  • Test-retest reliability
  • Inter-item reliability
• Validity

  The main extent to which a concept, conclusion or measurement is well-founded and likely corresponds accurately to the real world
• Internal validity


  • The extent to which the way the experiment was conducted supports the conclusion that the independent variable caused any observed differences in the dependent variable
• External validity

  • The extent to which the way the experiment was conducted supports generalizing the results to people and situations beyond those actually studied
• Construct validity


  The quality of the experiment's manipulations or operationalization of the research question
• Statistical validity


  The proper statistical treatment of data and the soundness of the researchers' statistical conclusions