CHAPTER 9: BASIC BETWEEN-SUBJECTS DESIGN

• Experimental design


  The plan for testing a hypothesis, the experiment's structure or floor plan, not the specific content
• We can use the same design to investigate different hypotheses
• Factors that determine an experimental design

  • The number of independent variables in the hypothesis
  • The number of treatment conditions needed to fairly test
  • Whether the same subjects are used in each of the treatment conditions
• Between-subjects design


  A subject participates in only one condition of the experiment
• Generalizability


  The representatives of our sample determine whether we can generalize our results to the entire population from which the sample was drawn
• Random sampling


  Increases an experiment's external validity
• Minimum number of subjects per group

  10 to 20 subjects in each treatment condition to detect a strong treatment effect
• Effect size


  A statistical estimate of the size or magnitude of a treatment effect, the larger the effect size the stronger the relationship between the independent and dependent variables and the fewer subjects needed to detect a treatment effect
• Effect size


  Determines the number of subjects required to detect a treatment effect
• Two-group design


  Involves the creation of two separate groups of subjects
• Two-independent groups design


  One IV with two levels and subjects are randomly assigned to one of the two conditions
• Random assignment


  Assigning subjects to conditions so that each subject has an equal chance of participating in each condition, to equally distribute subject variables between the treatment groups to prevent them from confounding an experiment
• Experimental condition


  Presents a value of the independent variable
• Control condition


  Presents a zero level of the independent variable
• Two experimental groups design


  Assign subjects to one of the two levels of the independent variable