week 7 & 8
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Questions and Answers

What is a key characteristic of between-subjects experimental designs?

  • The same participants are used in all conditions.
  • It involves repeated measures of the same participants.
  • It minimizes individual differences among participants.
  • Each participant contributes one score only. (correct)
  • Which statistical test would be appropriate for analyzing data from a between-subjects design with three conditions?

  • Chi-square test
  • One-way ANOVA (correct)
  • Independent samples t-test
  • Paired t-test
  • What is an advantage of using a between-subjects design?

  • It requires fewer participants than within-subjects designs.
  • Results are less influenced by time-related factors. (correct)
  • No practice effects occur.
  • It eliminates all potential confounding variables.
  • What is a common disadvantage of between-subjects designs?

    <p>They may be vulnerable to individual differences.</p> Signup and view all the answers

    How can researchers avoid selection bias in between-subjects designs?

    <p>Use random selection or matching methods.</p> Signup and view all the answers

    What is a specific problem that can arise with special populations in between-subjects designs?

    <p>Limited generalizability to the population.</p> Signup and view all the answers

    Which of the following describes a 'within-subjects' design?

    <p>The same participants are tested across multiple conditions.</p> Signup and view all the answers

    Which effect is NOT a concern in a between-subjects design?

    <p>Order effects</p> Signup and view all the answers

    What specific confounding variable might be addressed by holding gender constant in a between-subjects study?

    <p>Individual differences</p> Signup and view all the answers

    Which of the following statements is true regarding the use of a between-subjects design?

    <p>It helps avoid order effects by using different participants.</p> Signup and view all the answers

    What is the main purpose of statistical tests in the context of variance?

    <p>To evaluate the ratio of between-group variance to within-group variance</p> Signup and view all the answers

    Which of the following methods can minimize individual differences?

    <p>Using the same location for all participants</p> Signup and view all the answers

    What is a consequence of compensatory equalization in experimental design?

    <p>Control group demands equal treatment</p> Signup and view all the answers

    Which threat to internal validity is associated with participants giving up when they learn about differences in treatment?

    <p>Resentful demoralisation</p> Signup and view all the answers

    What is an advantage of using within-subjects design?

    <p>Reduction of time-related factors</p> Signup and view all the answers

    Which statistical test would be appropriate for analyzing data from repeated measures with three or more conditions?

    <p>Repeated-measures ANOVA</p> Signup and view all the answers

    How does maturation affect the validity of an experiment's results?

    <p>It causes changes unrelated to the treatment.</p> Signup and view all the answers

    What does regression to the mean imply in the context of testing participants?

    <p>Extreme scores will tend toward average on retests.</p> Signup and view all the answers

    Which issue could arise from uncontrolled time-related factors in an experiment?

    <p>Apparent changes due to age development</p> Signup and view all the answers

    What is the main disadvantage of a within-subjects design?

    <p>Vulnerability to order effects</p> Signup and view all the answers

    Study Notes

    Between-subjects Methods

    • Two Types of Experimental Designs:

      • Between-subjects: Different participants in each condition. Also known as "independent measures."
      • Within-subjects: Same participants in each condition. Also known as "repeated measures."
    • Data in Between-subjects:

      • Only 1 score per participant.
    • Statistical Analysis for Between-subjects:

      • 2 conditions: Independent samples t-test.
      • 3+ conditions: One-way ANOVA

    Advantages of Between-subjects Designs

    • Not influenced by time-related factors (history effects, maturation)
    • Not influenced by order effects (practice, fatigue)

    Disadvantages of Between-subjects Designs

    • Requires larger number of participants (problem with special populations)
    • Vulnerable to confounds (threats to internal validity):
      • Individual differences: Unique characteristics of each participant
      • Environmental variables: Changes in the testing environment, e.g., temperature, noise
    • Difficult to avoid selection bias (creating equal groups)

    Avoiding Selection Bias in Between-subjects Designs

    • Restricted randomisation: Creating equal groups.
      • Hold variables constant: Restricting the range of a variable.
        • Example: Only male participants.
      • Match for a potential confound: Participants are matched based on a potential confound variable.
        • Example: Matched based on age or IQ.
    • Block randomisation: Assign participants to groups randomly, but ensuring that older participants are evenly distributed across groups.
      • Example: Participants are randomly assigned to groups based on the flip of a coin. If the oldest participants are assigned to group 1 by the coin flip, the oldest remaining participants are assigned to group 2, and so on.

    Reducing Environmental Threats to Internal Validity in Between-subjects Designs

    • Run participants at the same time of day.
    • Use the same location for testing.

    Other Threats to Internal Validity in Between-subjects Designs

    • Differential attrition: Differences in attrition rates between groups.
      • Example: More participants drop out of one group, leaving samples of unequal size.
    • Diffusion: The treatment being spread from the experimental group to the control group.
      • Example: Participants in the control group learn about the treatment being received by the experimental group and start to use it themselves.
    • Compensatory equalisation: Participants demand similar treatment in the control group as the experimental group.
      • Example: The control group demands the same treatment as the experimental group.
    • Compensatory rivalry: Participants in the control group try harder to perform well to prove they are as good as the treatment group.
      • Example: Control group members might work harder to compensate and show that they can perform just as well as those in the treatment group.
    • Resentful demoralisation: Control group participants become less productive and motivated when they learn about the treatment received by the experimental group.
      • Example: Members of the control group become less productive, leading to a lower difference between groups than would otherwise be expected.

    Within-subjects Methods

    • Also known as: Repeated measures.

    Advantages of Within-subjects Designs

    • Removes or reduces threats from individual differences.
    • No threat from selection bias (same participants).
    • Avoids increased variance.
    • Fewewr participants needed, which increases statistical power.

    Disadvantages of Within-subjects Designs

    • Vulnerable to environmental threats (e.g., time-related factors)
    • Vulnerable to order effects (e.g., practice, fatigue).

    Analysis of Within-subjects Designs

    • 2 conditions: Paired-samples t-test (Wilcoxon for non-parametric data).
    • 3+ conditions: Repeated-measures ANOVA (Friedman’s ANOVA for non-parametric data).

    Time Threats in Within-subjects Designs

    • History effects: Differences in results due to events that occur between measurements.
      • Example: News reports about a new treatment could affect participants' wellbeing.
    • Maturation: Changes in results due to participants getting older or developing over time.
      • Example: Participants might become more experienced or mature, which could affect their performance on a task.
    • Regression to the mean: Extreme scores (high or low) may be less extreme when measured again.
      • Example: Participants who score extremely well on a test initially may improve or not perform as well when tested on that same test again. This trend is not necessarily due to the intervention.
    • Instrumentation: Changes in the measurement tools or procedures between measurements.
      • Example: Changing the scoring criteria for a test could influence the results.

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