Ch9-12 Summary

• Experiment


  A research investigation in which conditions are controlled
• Subjects


  The sampling units for an experiment, usually human respondents who provide measures based on the experimental manipulation
• Experimental Condition


  One of the possible levels of an experimental [independent] variable manipulation
• Blocking Variable


  Categorical variables included in the statistical analysis of experimental data as a way of statistically controlling or accounting for variance due to that variable
• Covariate


  A continuous variable included in the statistical analysis as a way of statistically controlling for variance due to that variance
• Main Effect


  The experimental difference in dependent variable means between the different levels of any single experimental variable
• Interaction Effect


  Differences in dependent variable means due to a specific combination of independent variables
• Summary of Experimental Characteristics

  • Experiments use subjects instead of respondents
  • Experimental variables become the key independent variables
  • Experimental effects exist to the extent that treatment groups exhibit differences between means
• Basic Issues in Experimental Design

  • Manipulation of the independent variable
  • Selection and measurement of the dependent variable
  • Selection and assignment of experimental subjects
  • Control over extraneous variables
• Independent Variable


  A variable with values that can be manipulated, or altered, independently of any other variable
• Experimental Treatment


  The term referring to the way an experimental variable is manipulated
• Categorical Variable


  Take on a value to represent some classifiable or qualitative aspect. Described by class or quality
• Continuous Variables


  They can take on any value. The researcher must select appropriate levels of that variable as experimental treatments. Described by quantity (level)
• Experimental Group


  A group of subjects to whom an experimental treatment is administered
• Control Group


  A group of subjects to whom no experimental treatment is administered
• Cell


  Refers to a specific treatment combination associated with an experimental group
• Dependent Variable


  The criterion by which the results of an experiment are judged; a variable expected to be dependent on the experimenter's manipulation of the independent variable
• Test Units


  The subjects or entities whose responses to the experimental treatment are measured or observed
• Systematic or Non-sampling Error


  Occurs if the sampling units in an experimental cell are somehow different than the units in another cell, and this difference affects the dependent variable
• Overcoming Sampling Errors


  • Randomization
  • Matching
  • Repeated Measures
  • Control Over Extraneous Variables
• Confound


  An experimental confound means that there is an alternative explanation beyond the experimental variables for any observed differences in the dependent variable
• Demand Characteristic


  Experimental design element or procedure that unintentionally provides subjects with hints about the research hypothesis
• Demand Effect


  Occurs when demand characteristics actually affect the dependent variable
• Experimenter Bias


  Occurs when an experimenter's presence, actions, or comments influence the subjects' behavior or sway the subjects to slant their answers in cooperation
• Reducing Demand Characteristics


  • Use an experimental disguise
  • Isolate experimental subjects
  • Use a "blind" experimental administrator
  • Administer only one treatment level to each subject
• Placebo


  A false experimental treatment disguising the fact that no real treatment is administered
• Placebo Effect


  The effect in a dependent variable associated with the psychological impact that goes along with knowledge of some treatment being administered
• Constancy of Conditions


  Means that subjects in all experimental groups are exposed to identical conditions except for the differing experimental treatments
• Counterbalancing


  Attempts to eliminate the confounding effects of order of presentation by requiring that one fourth of the subjects be exposed to treatment A first, one fourth to treatment B first, one fourth to treatment C first, and finally one fourth to treatment D first
• Basic versus Factorial Experimental Designs

  • Basic experimental designs: A single independent variable is manipulated to observe its effect on a single dependent variable
  • Factorial experimental designs: Are more sophisticated than basic experimental designs and allow for an investigation of the interaction of two or more independent variables
• Laboratory versus Field Experiments

  • Laboratory Experiment: Artificial, Low Realism, Few Extraneous Variables, High control, Low Cost, Short Duration, Subjects Aware of Participation
  • Field Experiment: Natural, High Realism, Many Extraneous Variables, Low control, High Cost, Long Duration, Subjects Unaware of Participation
• Within-Subjects Design


  Involves repeated measures because with each treatment the same subject is measured
• Between-Subjects Design

  Each subject receives only one treatment combination
• Internal Validity


  Exists to the extent that an experimental variable is truly responsible for any variance in the dependent variable
• Extraneous Variables Affecting Internal Validity

  • History
  • Maturation
  • Testing
  • Instrumentation
  • Selection
  • Mortality
• External Validity


  Is the accuracy with which experimental results can be generalized beyond the experimental subjects
• Attention Filters


  Are items that have known and obvious answers included just to see if participants are playing along
• Student Surrogates


  Students are easily accessible, but they often are not representative of the total population
• Examples of Quasi-Experimental Designs

  • One Shot Design (After Only)
  • One Group Pretest–Posttest
  • Static Group Design
• Alternative Experimental Designs


  • Pretest–Posttest Control Group Design (Before–After with Control)
  • Posttest Only Control Group (After-Only with Control)
  • Compromise Designs