Chapter 8: Experimental Design Flashcards

1
Q

Extraneous and Confounding Variables —Key Points—

A

Main point: Most outcomes are influenced by multiple variables

  • Purpose of experiments is to isolate the causal factor
  • Other factors that influence the DV are problematic
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2
Q

Extraneous Variables

A

Variables other than the IV that could affect the outcome/DV

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3
Q

Confounding Variables

A

An extraneous variable that that varies systematically with the IV

A confounding variable makes it impossible to claim causation from IV

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4
Q

Extraneous Vs. Confounding Variables

A

Extraneous Variables generally just add variability, while Confounding Variables can create misleading conclusions about causality.

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5
Q

Test Prep — Identify the Confounding Variable:

Research Question: Does explaining to someone else enhance comprehension?
* Explanation condition: Read an article about echolocation in bats (10 min). After reading the article once, attempt to explain it to someone else, with access to the article the whole time (10 min).
* No explanation condition: Read an article about echolocation in bats (10 min).
* DV: Take a test that measures comprehension (both groups get this test, obvi).

  1. Identify the confounding variable.
  2. Describe why/how that confounding variable disrupts internal validity
  3. Fix the experiment
A

Answers:

  1. Confounding variable: Time with the article
    (The explanation group has TWICE the amount of time with the article, compared to the control group…)
  2. Disruption of Internal Validity: If participants in the explanation condition score better than participants in the no explanation condition, we don’t know if (a) explanation improves comprehension, (b) extra study time improves comprehension, or (c) both.
  3. Fix the experiment:
    Ensure both groups spend the same amount of time with the material. For example:
    a) Explanation condition: Read for 10 minutes, then explain for 10 minutes.
    b) No explanation condition: Read for 10 minutes, then engage in another active task related to the material for 10 minutes (e.g., summarizing in writing or answering questions about the article).

This adjustment controls for time and engagement differences, isolating the effect of explaining on comprehension.

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6
Q

Confounding Variables Relationship to Internal Validity

A

Confounding Variables = a THREAT to Internal Validity!!!

  • Internal Validity only exists when the results of an experiment can be confidently attributed the effect of the IV.
  • When a confounding variable is present, we cannot determine which variable is responsible for the effect
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7
Q

Basic Experiment Types:

A

Between-Subjects Design: Each group/participant experiences ONE condition
* Between-Subjects Design = Independent Groups Design

Within-Subjects Designs: Each participant experiences ALL conditions (only one group).
* Within-Subjects Designs = Repeated Measures Desig

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8
Q

Assigning participants to conditions: Between-subjects/Independent Groups Design

A
  • Subjects are randomly assigned.
  • Random assignment prevents systematic biases
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9
Q

Assigning participants to conditions: Within-subjects/Repeated Measures Design

A

All subjects experience every conditions

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10
Q

Assigning participants to conditions: Matched pairs Design

A

Participants are paired/matched based on similar participant variables (ie: age, sex, hight, etc.) before being assigned a condition.

Ensures that the groups are equivalent (on the matching variable) before introducing the IV manipulation.

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11
Q

Advantages & Disadvantages of Within-Groups Designs

A

Advantages:
* More confidence when making statistical inferences
* Fewer subjects required

Disadvantages:
* Potential Risk of Order Effects

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12
Q

Order Effects

A
  • Practice/learning effect
  • Fatigue effect
  • Carryover effect:
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13
Q

Practice/ Learning Effect

A

Definition: Performance increases due to practice in the experiment (warm-ups)

Solution: reduced by adding pre-experimental practice trials

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14
Q

Fatigue Effect

A

Definition: Performance decreases due to fatigue

Solution: Reduced by allowing breaks during the experiment

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15
Q

Carry-Over Effect

A

Definition: Persistent influence of one level of the IV on the next level of the IV

Solution: Reduced by allowing breaks during the experiment

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16
Q

Controlling for Order Effects

A

Counterbalancing and Randomization

17
Q

Counterbalancing

A

A method of controlling for order effects in a repeated measures design by switching (balancing) the match between condition and stimuli

18
Q

Randomization

A

randomly determining the order for each subject

19
Q

Matched Pairs Design: When are they Useful?

A

When a specific participant variable is very likely to affect the DV

When the sample size is NOT particularly large

20
Q

Pretest Design

A

Testing the level of the DV before introducing the IV

  • Reveals weather or not participant groups are fair/the same
21
Q

Posttest Design

A

A typical experiment uses a post test design. Testing the level of the DV after introducing IV

22
Q

Pretest-Posttest Design

A

Measure the DV before introducing the IV and then measure the DV again after IV is introduced