Chapter 9

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1

within-subjects experimental design OR

repeated-measures experimental design

compares two or more different treatment conditions by observing or measuring the same group of individuals in all of the treatment conditions being compares

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  • Confounding from environmental variables
  • Confounding from time-related variables
    • H.E.R.M.I.T.

threats to internal validity to Within-subjects experiments

3

counterbalancing

defined as changing the order in which treatment conditions are administered from one participant to another so that the treatment conditions are matched with respect to time.

4

History

threat to internal validity by any differences that are observed between treatment conditions may be caused

5

Instrumentation

refers to changes in the measuring instrument that occur during a research study in which participants are measured in a series of treatment conditions

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Regression toward the mean

mathematical phenomenon in which extreme scores on one measurement tend to be less extreme on a second measurement

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Order effects

when the experience of having tested in one treatment condition (participating and being measured) has an influence on the participants' scores in a later treatment condition

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carry-over effects

occur when one treatment condition produces a change in the participants that affects their scores in subsequent treatment conditions

9

progressive error

refers to changes in a participant's behavior or performance that are related to general experience in a research study but not related to a specific treatment or treatments

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counterbalancing

defined as changing the order i which treatment conditions are administered from one participant to another so that the treatment conditions are matched with respect to time.

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  • counterbalancing increases variance
  • asymmetrical order effects
  • ^ # of treatments creates order effects w/ counterbalancing

limitations of counterbalancing

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complete counterbalancing

present treatments in every possible sequence. A particular series of treatment conditions may create its own unique order effects.

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latin square

used to construct a simple unbiased procedure for selecting sequences

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  • individual differences
  • time-related factors
  • fewer participants

three factors that differentiate within-subjects from between-subjects

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matched-subjects design

each individual in one group is matched with a participant in each of the other groups. the individuals are equivalent with respect to a variable that the researcher considers to be relevant

duplicates all the advantages of a within and between w/o the disadvantages of either one

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two-treatment design

a researcher can easily maximize the differences between treatments by selecting two treatment conditions that are clearly different

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multiple-treatment design

a researcher can create a series of conditions and then observe how the participants' behavior changes as they move through the series of treatments. it also produces a more convincing demonstration of cause and effect relationship than is provided by a two-treatment.