Internal validity

• A type of evaluation of the experiment that asks whether your IV is the only possible explanation of the results shown for your DV

• Researchers go to lengths to increase internal validity.. -

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Threats to internat validity:

• I) history:. Events that occur between the DV measurements in a repeated-measure design

• 2)Maturation: changes in participants (maturation, fined , on, boxed )

• 3) testing: "practice effect “ S change that occurs because measuring the DV causes a change in the DV

• (Reactive measures: DV measurement changes the DV being measured > people's attitudes about women's issue Makes me answer that ) way . ) non-reactive measure, hidden cameras, deception

• 4) instrumentation (instrument decay ): I changes in the measurement of the DV that are due to the measuring (machine or human) - if a experimental gets tired of measuring 6 affects results.

• 5) statical regression: if you remeasure participants who have extreme scores their first time, their subsequent scores one likely to regress toward the mean.

• 6) selection: if participants are chosen in such a way that the groups are not equal before the experiment started, we cannot be sure our is what caused IV different caused our differences

• 7) mortality (attrition): if experimental participants from different groups drops out of the study at different rates

• 8) interactions with selection: there are systematic differences between selected treatment groups based on maturation, history or instrumentation

  • e.g. : 2 preschools with birth records of healthy born on time 2020 - 2021 preschool I: rock island → curriculum 3-4 & preschool 2: pleasant valley → 3-4 curriculum. The problem comes in when the a different places have different socioeconomic differences &: time between birth + preschool

• 9) diffusion or imitation of treatment: occurs if participants in one - treatment group become familiar with what stud the other group was doing

  • e.g.:

Internal validity is the most important property of any experiment

External validity:

• The type of evaluation of an experiment wherein the determination is made about if the experimental results apply to populations & situations that are different from those of the experiment