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Topics Appropriate to Experiments

Topics Appropriate to Experiments. Projects with limited and well-defined concepts. Projects that are exploratory rather than descriptive. Studies of small group interaction. Components of Experiments. Independent and dependent variables Pretesting and posttesting

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Topics Appropriate to Experiments

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  1. Topics Appropriate to Experiments • Projects with limited and well-defined concepts. • Projects that are exploratory rather than descriptive. • Studies of small group interaction.

  2. Components of Experiments • Independent and dependent variables • Pretesting and posttesting • Experimental and control groups • Stimulus and no stimulus

  3. Experimental andControl Groups • Must be as similar as possible. • Control or Comparison group represents what the experimental group would have been like had it not been exposed to the stimulus.

  4. Experiment

  5. Two & Half Men • Short clip making fun of the experimental design in testing drugs

  6. Selecting Subjects • Probability sampling • Randomization • Matching

  7. Randomization and Matching • May not know which variables will be relevant for matching process. • Most statistics used to analyze results assume randomization. • Randomization only makes sense if you have a large pool of subjects.

  8. Internal Validity • Refers to the possibility that the conclusions drawn from experimental results may not accurately reflect what went on in the experiment itself. • Did something other than the experimental stimulus affect the dependent variable?

  9. Sources of Internal Invalidity • Historical events may occur during the course of the experiment. • Maturation of the subjects. • Testing and retesting can influence behavior. • Instrumentation

  10. Sources of Internal Invalidity • Selection biases. • Experimental mortality - subjects drop out of the study before it's completed.

  11. External Validity • Refers to the possibility that conclusions drawn from experimental results may not be generalizable to the “real” world. • Is the experimental setting unrealistic? • Is pre-testing influencing the subjects (i.e. cueing them in on what the researcher wants)

  12. Limiting External Invalidity Solomon Four Group Design - Four groups of subjects, assigned randomly: • Groups 1 and 2 are the control and experimental group. • Group 3 does not have the pre-test. • Group 4 is only posttested.

  13. Solomon Four-Group Design • G1:Pretest-stimulus-posttest • G2:Pretest-posttest • G3:Stimulus-posttest • G4:posttest

  14. Solomon Four-Group Design

  15. Example • Champney and Edleman. 2010. “Assessing Student Learning Outcomes in United States Government Courses” • Available on WebCampus (not required reading).

  16. Posttest-only Control Group Design • Includes Groups 3 and 4 of the Solomon design. • With proper randomization, only these groups are needed to control problems of internal invalidity and the interaction between testing and stimulus. • Commonly done in the social sciences

  17. Web-based Experiments • Increasingly, researchers are using the World Wide Web to conduct experiments. • Because representative samples are not essential in some experiments, researchers use volunteers who respond to invitations online.

  18. Experimental Method Strengths: • Isolation of the experimental variable over time. • Experiments can be replicated several times using different groups of subjects.

  19. Experimental Method Weaknesses: • Artificiality of laboratory setting. • Social processes that occur in a lab might not occur in a more natural social setting.

  20. Example of Experiments in Political Science • Mendelberg, Tali. 1997. Executing Hortons: Racial Crime in the 1988 Presidential Campaign. The Public Opinion Quarterly 61(1, Spring): 134-157. • Available on WebCampus (not required reading).

  21. Methodology • Experiment • 77 white students at U of M • Median age was 18 • Treatment group shown the ad, control group was not • OLS regression (not a T-test)

  22. Findings • Students shown the Horton ad were more likely to have negative views on race and racial policies • Students shown the Horton ad did not have different views on crime

  23. The End • Read Levin and Fox Ch. 7 • Will go over homework assignment • Read Matland, Richard E. 1994. “Putting Scandinavian Equality to the Test: An Experimental Evaluation of Gender Stereotyping of Political Candidates in a Sample of Norwegian Voters.” British Journal of Political Science 24, 2: 273-92. • Available on WebCampus

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