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Research Methods:�Experimentation

Mr. Koch

AP Psychology

Andover High School

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Experimental Method

An experiment is a method that allows scientists to establish cause and effect. It explores the relationship between the independent variable (IV) and the dependent variable (DV). It begins by establishing operational definitions for the hypothesis. Then it manipulates the experimental condition to test the hypothesis. Experiments also often contain a control condition, in which a control group is exposed to all the same factors as the experimental subjects except the experimental condition.

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Who is participating in the experiment?

  • How do we choose our sample from our population?
    • Representative Sample – accurately reflects larger population

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      • Random Sampling

vs.

      • Convenience Sampling
        • Greater potential for sampling bias

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    • Does our sampling method allow the results of our study to be generalized?

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*Note: Using a pre-selected or stratified sample would technically make the study a quasi-experiment.

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Experimentation

  • Replication of studies is essential in science. (Other researchers can retest your hypothesis for procedural and outcome validity.)

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  • Research should be evaluated through the peer review process by other qualified professionals in the same field.

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  • Psychological research should have external (ecological) validity, focusing on processes that occur in real-life environments.

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Experimental Method

  • The experimental method is the most commonly used testing method in psychology because it is accurate and controlled.

  1. Hypothesis
      • A specific, testable proposition about something to study
          • often based on previous research
      • States a relationship between 2 variables (any condition or behavior that can change in quantity/quality)
      • “If – Then”
      • Should be falsifiable

Example:

“If students sleep less before the exam, then their grades on the exam will be lower.”

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Experimental Method

2. Independent Variable (IV)

      • Controlled and manipulated by the experimenter to determine how it affects the dependent variable (If…)
      • It causes the resulting changes

3. Dependent Variable (DV)

      • Changes in response to the independent variable (Then…)
      • What is being measured
      • It is dependent upon the IV

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A reduced amount of sleep will result in lower test scores among students.

(IV) (DV)

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Experimental Method

4. Experimental Group (Condition)

      • The group in which the condition under study is present

5. Control Group (Condition)

      • Altered condition is not present
        • baseline for comparison

6. Random Assignment

      • Participants have an equal likelihood of being assigned to any particular condition
          • “Random assignment” vs. “Random Sample”

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Experimental Method

7. Controlled Variable

      • Any variable that is held constant among all subjects
        • Reduces possibility of alternative explanations

8. Confounding Variable

      • Any variable that is not controlled and could possibly affect the validity of the results

9. Theory

      • A general principle based on information to explain what is learned
        • Can be retested for validity

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Experimentation

  • Additional terms:
    • Placebo Effect
      • Experimental results caused by participant’s expectations, rather than actual treatment/condition
    • Single-blind design
      • Study in which participant is unaware of placement in experimental or control group

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    • Experimenter Bias
      • Unintentional effects experimenters may exert on their results
    • Double-blind design
      • Study in which neither the experimenter nor the participant knows if the subject is in the experimental or control group

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Experimenter Bias?...

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Ethics

  • Because psychologists have an ethical obligation to protect the dignity and welfare of the people who participate in research, the APA has drawn up a set of ethical principles to guide research.

  • The code sets up 4 main conditions:
      • Informed consent/assent
      • Protection from harm
      • Confidentiality
      • Debriefing (especially when deception is used)

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  • Researchers must also follow federal regulations and guidelines of local institutional review boards.
  • Research that cannot ethically be done with humans can sometimes be performed on animals.

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