External Validity in Experimental Design
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Questions and Answers

What is generalisation?

Does the IV represent the concept we intend?

A measure is externally valid if what?

It truly measures the hypothetical construct intended.

An experiment is externally valid if it is similar to what?

Phenomena in the real world.

High external validity means what negative thing?

<p>Lack of control of confounds.</p> Signup and view all the answers

What are the two types of external validity?

<p>Population validity and ecological validity.</p> Signup and view all the answers

Explain population validity.

<p>Extent to which results can be generalized from experimental sample to a defined population.</p> Signup and view all the answers

Explain ecological validity.

<p>Extent to which results can be generalized from set of environmental conditions in an experiment to other environmental conditions.</p> Signup and view all the answers

What are the threats to external validity?

<p>Reactive effects of testing, reactive effects of experimental setting, selection-treatment interaction, multiple-treatment interference.</p> Signup and view all the answers

What are reactive effects of testing?

<p>Occurs whenever a pre-test increases or decreases the respondents' sensitivity to the treatment.</p> Signup and view all the answers

When do reactive effects of experiment arrangements occur?

<p>When conditions of a study are such that results are not likely to be replicated in non-experimental situations.</p> Signup and view all the answers

Give examples of reactive effects.

<p>Hawthorn effects, novelty effects, experimenter effects, Rosenthal effect.</p> Signup and view all the answers

What are Hawthorn effects?

<p>Experiment in a factory, where awareness of being observed affects productivity.</p> Signup and view all the answers

What are novelty effects?

<p>People find experimental tasks novel and interesting, which raises their motivation and affects performance.</p> Signup and view all the answers

What are experimenter effects?

<p>When an interviewer inadvertently influences a participant's responses by suggesting expectations.</p> Signup and view all the answers

What are Rosenthal effects?

<p>Participants behave in a way that fulfills experimenters' expectations, potentially skewing results.</p> Signup and view all the answers

What is selection-treatment interaction?

<p>Possibility that some characteristics of participants interact with some aspects of treatment.</p> Signup and view all the answers

What is multiple-treatment interference?

<p>When participants receive more than one treatment, influencing subsequent effects.</p> Signup and view all the answers

How can external validity be improved?

<p>Replication and replication with extension.</p> Signup and view all the answers

What is replication?

<p>Additional scientific study conducted in the same manner as the original research.</p> Signup and view all the answers

What is replication with extension?

<p>Experiment seeks to replicate previous findings but does so in a different setting or conditions.</p> Signup and view all the answers

What are threats to statistical validity?

<p>Making a type I error.</p> Signup and view all the answers

What are possible causes of type I errors?

<p>Fishing (lots of tests on data).</p> Signup and view all the answers

What is a type II error?

<p>Failing to reject the null when the null is false.</p> Signup and view all the answers

Study Notes

Generalization and External Validity

  • Generalization refers to the extent to which findings from an experiment can be applied to broader contexts or groups.
  • A measure is considered externally valid if it accurately represents the hypothetical construct it intends to measure.

External Validity in Experimental Design

  • An experiment is externally valid if it closely resembles phenomena observed in real-world situations.
  • High external validity, often seen in field experiments, can lead to a lack of control over confounding variables.

Types of External Validity

  • Population validity indicates how well results can be generalized from the experimental sample to the overall population.
  • Ecological validity assesses the generalization of results from the specific environmental conditions of the experiment to other settings.

Threats to External Validity

  • Four key threats compromise confidence in generalizing study results:
    • Reactive effects of testing
    • Reactive effects of experimental settings
    • Selection-treatment interaction
    • Multiple-treatment interference

Reactive Effects of Testing

  • These effects occur when a pre-test influences respondents' sensitivity toward the treatment, skewing true results.

Experimental Arrangements and Their Effects

  • Reactive effects from experimental arrangements arise when the study conditions compromise the replicability of results in non-experimental environments.

Examples of Reactive Effects

  • Examples include:
    • Hawthorn Effects: Behavior changes due to awareness of being observed during studies (e.g., changes in productivity based on observation).
    • Novelty Effects: Increased motivation and performance due to the novelty of the experimental task.
    • Experimenter Effects: Influences from experimenters that shape participants' responses towards hypotheses.
    • Rosenthal Effects: Self-fulfilling prophecies where participants adjust behavior to align with expectations.

Selection-Treatment Interaction

  • This interaction occurs when certain characteristics of study participants, chosen without random sampling, affect treatment outcomes (e.g., past experiences or personality traits).

Multiple-Treatment Interference

  • Arises when participants receive multiple treatments, potentially influencing subsequent responses due to former exposures (includes sequence and carry-over effects).

Improving External Validity

  • External validity can be enhanced through:
    • Replication: Conducting additional studies in the same manner as the original.
    • Replication with extension: Replicating findings in different settings, using different participants, or under varied conditions.

Statistical Validity Issues

  • Threats to statistical validity include type I errors, which occur when the null hypothesis is incorrectly rejected (false positives).
  • Type I errors can result from practices like extensive "fishing" (conducting multiple tests on the same dataset).

Type II Errors

  • A type II error is the failure to reject the null hypothesis when it is actually false, indicating missed findings in research.

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Description

This quiz delves into the concept of external validity in experimental design, focusing on its significance, types, and threats. Understand how generalization and ecological factors play a crucial role in assessing the applicability of research findings across different contexts and populations.

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