PSY 220 Ch. 8: Experimental Design

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ralejo
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PSY 220 Ch. 8: Experimental Design
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2012-11-03 18:43:38
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PSY 220 Experimental Design Needham
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PSY 220 Experimental Design Needham
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  1. Attrition (mortality)
    The loss of subjects who decide to leave an experiment.
  2. Between-subjects design (Independent groups design)
    An experiment in which different subjects are assigned to each group.
  3. Carry-over effect
    A problem that may occur in repeated measures designs if the effects of one treatment are still present when the next treatment is given.
  4. Confounding variable
    • A variable that is not controlled in a research investigation.
    • In an experiment, the experimental groups differ on both the independent variable and the confounding variable
  5. Counterbalancing
    A method of controlling for order effects in a repeated measures design by either including all orders of treatment presentation or randomly determining the order for each subject
  6. Fatigue effect
    The experiment is far to physically draining for the individual that they give up thus not displaying the desired behaviours.
  7. Independent groups design (Between-subjects design)
    An experiment in which different subjects are assigned to each group.
  8. Internal validity
    The certainty with which results of an experiment can be attributed to the manipulation of the independent variable rather than to some other, confounding variable.
  9. Latin square
    A technique to control for order effects without having all possible orders.
  10. Learning effect (practice effect)
    Influences on performance that arises from a practicing a task
  11. Matched pairs design
    A method of assigning subjects ti groups in which pairs of subjects are first matched on some characteristic and then individually assigned randomly to groups.
  12. Mortality (attrition)
    • The loss of subjects who decide to leave an experiment
    • Mortality is a threat to internal validity when the mortality rate is related to the nature of the experimental manipulation.
  13. Order effect
    In a repeated measures design, the effect that the order of introducing treatment has on the dependent variable.
  14. Posttest-only design
    A true experimental design in which the dependent variable (Posttest) is measured only once, after manipulation of the independent variable.
  15. Pretest-posttest design
    A true experimental design in which the dependent variable is measured both before (pretest) and after (posttest) manipulation of the independent variable.
  16. Random assignment
    Use of a random "chance" procedure (such as a random number generator or coin toss) to determine the condition in which an individual will participate.
  17. Repeated measures design (within-subjects design)
    An experiment in which the same subjects are assigned to each group.
  18. Selection differences
    • Differences in the type of subjects who make up each group in an experimental design
    • This situation occurs when participants elect which group they are to be assign to.
  19. Within-subjects design (Repeated measures design)
    An experiment in which the same subjects are assigned to each group.
  20. Define confounding variable, and describe how confounding variables are related to internal validity.
    • Confounding variable: a variable that is not controlled in a research investigation.
    • A good experimental design requires eliminating possible confounding variables that could result in alternative explanations
    • To have internal validity, the researcher must conduct an experiment that only the independent variable can be the cause of the results.
  21. Describe the posttest-only design and the pretest-posttest design, including the advantages and disadvantages of each design.
    • Posttest-only design:
    • (1) Obtain two equivalent groups of participants
    • (2) Introduce the independent variable
    • (3)Measure the effect of the independent variable on the dependent variable.

    • Pretest-posttest design: Only difference is that a pretest is given before the experimental manipulation is introduced
    • Advantages:
    • 1. Enables researcher to assess whether the groups are equivalent to begin with
    • 2. Necessary to select the participants in the experiment
    • 3. Find the lowest or highest scorers
    • 4. Analysis of the group and individual differences
    • 5. Necessary whenever there is a possibility that participants will drop out of the experiment (most likely to occur in a study that lasts a long time) - attrition
    • Disadvantages:
    • 1. May be time-consuming and awkward to administer in the context of the particular experimental procedures being used.
  22. Contrast an independent groups design (between-subjects) design with a repeated measures (within-subjects) design.
    • Independent groups design (between-subjects): An experiment in which different subjects are assigned to each group.
    • Repeated measures design (within-subjects): An experiment in which the same subjects are assigned to each group.
  23. Summarize the advantages and disadvantages of using a repeated measures design.
    • Advantages:
    • 1. A reduction in te number of participants required to complete the experiment
    • 2. Greater control over participant differences and thus greater ability to detect an effect of the independent variable.
    • 3. Both conditions appear, and our responses occur in the context of exposure to both levels of the independent variable.

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