Threats to internal validity

Some threats to internal validity are…

History: Events that occur during the research study might impact the participants’ responses.
Maturation: Changes that occur naturally due to the passage of time – like aging or fatigue, can affect the outcome of an experiment.
Testing effect: The act of taking a test can change how participants perform on subsequent tests.
Instrumentation: Changes in the measurement instrument or in the observers or scorers may produce changes in outcomes.
Selection bias: If participants are not randomly selected, it may result in biased samples and potential threats to internal validity.
Attrition or Mortality: Participants dropping out before the study is completed can impact results and affect internal validity.
Statistical regression: Participants with extreme scores on a pretest will tend to score closer to the mean on a post-test, which might not be attributed to treatment effect.
Experimental treatment diffusion: When control group members are influenced by experimental group members and change their behavior accordingly.
Experimenter bias: The experimenter’s expectations can influence the findings if they subconsciously guide participants to respond in a certain way.
Hawthorne effect (Observer effect): Participants alter their behavior because they know they are being observed.
Order effects/Carryover effects: The order in which treatments are presented can influence participant responses.
Placebo effect: When participants respond differently just because they believe they received some sort of treatment.
Confounding variables: Any other variables that have an impact on the dependent variable, making it difficult to establish causal relationships.
Social desirability bias: Participants may respond in ways that make them look good socially rather than truthfully responding to items under study.
Demand characteristics: Cues that signal how participants should behave can influence their responses and threaten internal validity.
Pretesting effects/Sensitization: A pretest can influence how participants respond to the experimental treatment.

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