Common Threats to Validity

• Subject Characteristics

• Mortality

• Location

• Instrument

• Maturation

• Regression

• Hawthorne Effect

• History

• Implementation

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Subject Characteristics - Selected on a non-random basis; members of a certain group perhaps

Mortality - Loss of subjects: transfers, promotions, retirement, death

Location - Different environments have different resources or different distractions

Instrumentation -Problem with the testing instrument or observer

Maturation - Any change that occurs because of time passing

Regression -Move to the mean if participants were chosen specifically because of very high scores or very low scores

Hawthorne Effect - change simply because subjects were assigned to a treatment group. Can be a negative change (see text p. 197)

History - Unanticipated/unforeseen event. Sprinklers go off in the middle of the study. Blizzard closes down the company in the middle of the project.

Implementation -Flaw in the way a study was conducted