8.5: Other Threats to Internal Validity

• Differential Attrition

  A threat to internal validity that occurs when attrition in one group is systematically different from the attrition in another group.
• Diffusion

  A threat to internal validity that occurs when a treatment effect spread to the control group, usually from participants talking to each other.
• Compensatory Equalisation

  A threat to internal validity that occurs when an untreated group demands to receive a treatment that is the same as or equivalent to the treatment received by another group in the research study.