Experimental Research Strategy

1. Experimental Research Strategy Chapter 8 George S. Robinson, Jr., Ph.D. Department of Psychology North Carolina A&T State University

2. Experimental Research Strategy • Cause-and-effect relationships • changes in one variable are directly responsible for causing changes in the other variable • causation and the third-variable problem • causation and the directionality problem • controlling nature • to demonstrate a cause-and-effect relationship, one must control “nature” (other variables in the experiment)

3. Elements of an Experiment • Establish a cause-and-effect relationship between two variable • manipulation • change in one variable causes a direct change in the other variable • control • must rule out the possibility that the change is caused by another variable

4. Manipulation and Measurement • Manipulation is used to determine the direction of the cause-and-effect relationship • independent variable • levels - different values of the I.V. • dependent variable • measured variables • extraneous variables • all other variables in the experiment • treatment condition

5. Control and Extraneous Variables • Eliminate all confounding variables • prevent any extraneous variable from becoming a confounding variable • extraneous variable = confounding variable ONLY if it influences the dependent variable • extraneous variable - confounding variable ONLY if it varies systematically with the independent variable

6. Control and Extraneous Variables - cont. • Identifying extraneous variables • participant variables (e.g., age, gender, race, size, strength, IQ, etc.) • environmental variables (room temperature, time of day, different equipment, etc.)

7. Controlling Extraneous Variables • Holding a variable constant • standardize the environment and procedures • same room, same time of the day, same age, etc. • matching values across treatment conditions • match the levels of the variable across treatment conditions • balanced gender (10 males and 10 females in each treatment, balance time of day (half at 9:00, the other half at 5:00), etc. • control by randomization • randomization - use of a random process to help avoid a systematic relationship between two variables • random assignment - use of a random process to assign participants to treatment conditions

8. Control Groups • Control groups • no-treatment control group • a condition in which the participants do not receive the treatment • placebo control group • a condition in which the participants receive a placebo instead of the actual treatment

9. Manipulation Checks • Manipulation check • an additional measure to assess how the participants perceived and interpreted the manipulation • a second explicit measure of the independent variable (e.g., sleep deprivation measured by EEG to make sure the participants were sleep deprived) • give participants a questionnaire after the experiment (e.g., were you really sleepy?)

10. Increasing External Validity: Simulation and Field Studies • Simulation • the creation of conditions within an experiment that simulate or closely duplicate the natural environment in which the behaviors being examined would naturally occur • mundane realism versus experimental realism • e.g. prison study • field study • an experiment conducted in a place that the participants or subject perceives as a natural environment • e.g. bystander helping behavior