External Validity and Generalizability

Claims and Validity

  • Claims from research are invalid if the research itself is invalid.

  • Validities assess how well research is conducted.

External Validity

  • External validity assesses how well research results apply outside the study's specific context (participants, settings, situations).

  • The goal of most research is for the results to apply to the real world, not just the lab.

  • Poor external validity means the research doesn't generalize to real-world behavior.

  • Terms synonymous with external validity:

    • Generalizability: How general are the results?

    • Ecological validity: Would the same results occur in a real-world setting?

Aspects of External Validity

  • Sample and Population:

    • The tested group should represent the larger group you want to learn about.

    • A sample is a subset of the population.

  • Sample Size:

    • Need to test enough subjects to be representative.

    • Statistical power analysis can determine the necessary number of participants.

  • Sample Composition:

    • The sample should include a variety of people representative of the full population.

    • Consider factors like region, race, and gender.

  • College Sophomore Problem:

    • Much psychological research relies on college freshmen/sophomores.

    • This is mainly due to their easy accessibility at universities.

    • College students may not represent the broader population due to age, education level, etc.

Harlow's Monkey Experiments and External Validity

  • Do the behaviors of Harlow's monkeys represent the behavior of all monkeys or monkeys in the wild?

  • Does the behavior of Harlow's monkeys represent the behavior of humans?

    • It's assumed that monkeys are close enough to humans to generalize, but this may not be the case.

Real World Example: Colombian Peace Deal Vote

  • A peace deal was put to a national vote but was narrowly rejected.

  • Low voter turnout and a hurricane potentially skewed the sample, making it less representative.

  • This highlights how important a representative sample is for accurate results.

In the context of elections, the 'population' refers to the entire group of eligible voters, while a 'sample' is the group of people who actually vote (