PSYCH 2300 Chapter Notes - Chapter 11: Internal Validity, Measuring Instrument, Confounding
19 Aug 2016
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Threats to internal validity: did the independent variable really cause the difference: design confounds. Alternative explanation because experiment was poorly designed: selection effect. Different independent variable groups have different types of participants: order effect. Outcome might be caused by independent variable but also could be because of order in which levels presented: the really bad experiment (a cautionary tale) An experiment in which a researcher recruits one group of participants; measures them on pretest; exposes to treatment or intervention; measures on posttest: six potential internal validity threats in one-group, pretest / posttest designs. When observed change in an experimental group could have emerged more or less spontaneously over time. When it is unclear whether a change in treatment group is caused by historical factor or event that affects everyone or almost everyone in the group. A phenomenon in which any extreme finding is likely to be closer to its own typical or mean level the next time it is measured.
