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Attrition (mortality)
The loss of subjects who decide to leave an experiment.
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Between-subjects design (Independent groups design)
An experiment in which different subjects are assigned to each group.
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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.
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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
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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
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Fatigue effect
The experiment is far to physically draining for the individual that they give up thus not displaying the desired behaviours.
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Independent groups design (Between-subjects design)
An experiment in which different subjects are assigned to each group.
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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.
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Latin square
A technique to control for order effects without having all possible orders.
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Learning effect (practice effect)
Influences on performance that arises from a practicing a task
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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.
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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.
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Order effect
In a repeated measures design, the effect that the order of introducing treatment has on the dependent variable.
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Posttest-only design
A true experimental design in which the dependent variable (Posttest) is measured only once, after manipulation of the independent variable.
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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.
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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.
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Repeated measures design (within-subjects design)
An experiment in which the same subjects are assigned to each group.
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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.
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Within-subjects design (Repeated measures design)
An experiment in which the same subjects are assigned to each group.
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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.
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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.
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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.
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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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