6.3: Threats to External Validity

• Category 1: Generalising across participants or subjects.

  What are the five particular issues with category 1?

  1. Selection Bias
  2. College
  3. Volunteer Bias
  4. Participant Characteristics
  5. Cross-Species Generalisations.
• Category 2: Generalising Across Features of a Study

  What are the three issues regarding category 2?

  1. Novelty Effect: When individuals participating in a research study perceive and respond differently than they would in the normal, real world.
  2. Multiple Treatment Interference: Occurs when participants are exposed to more than one treatment and their responses are affected by an earlier treatment.
  3. Experimenter Characteristics: When the results of a study can be specific to an experimenter with a certain set of characteristics.
• Category 3: Generalising Across Features of the Measure

  What are the three issues regarding category 3?

  1. Sensitisation: A threat to external validity that occurs when the assessment procedures alters participants so that they react different to treatment than they would in the real world when the treatment is used without assessment.
  2. Generality Across Response Measures: Many variables can be defined and measured in different ways.
  3. Time of Measurement: In a research study, the scores for individuals are measured at a specific time after (or during) the treatment.