Problems for internal validity PDF

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Summary

Chris Dickinson...

Description

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Unsystematic variability – random across both groups o Systematic variability

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Confounding variables – “confuse”, confused about what is causing change in DV o Potential threat to internal validity

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Lack of impact/realism –

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Placebo effects – when participants improve because they believe they are receiving effective treatment

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Demand characteristics – when participants guess what the study is about and change their behavior in the expected direction

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Experimenter bias – experimenters expectations influence their interpretation of results

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Selection bias – the groups at the various levels of an IV contain different types of participants

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Attrition – when people drop out of a study over time

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Maturation – design with a pretest/posttest, a treatment group shows an improvement over time but is not clear whether the improvement was cause by the treatment or whether the group would have improved spontaneously, even without a treatment.

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History effects – an external, historical even happens for everyone in a study at the same time as the treatment variable.

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Retesting effect/instrumentation effects –participants tend to change as a result of having been tested before/a measuring instrument could change (person observing changes, 2 tests with one more difficult than the other)

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Regression towards the mean – when an extreme finding is caused by a combination of random factors that are unlikely to happen in the same combination again, so the extreme finding gets less extreme over time....