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Unformatted text preview: Page 2 of3 Page 3 of3 A Jnqior limitation of these designs is that they do not always possess a high level of internal validity. Internal validity is that there is a link between the Independent and Dependent variable,: "you got what you got because yOll did what you did". In terms of design. it means that the outcomes are sometimes not relnted to what the researcher thinks the conditions are. For example, the treatment to use a new teelmique for reading instructions may seem to have been effective, but the critical factor tums Ollt to be that the teacher smiled at the students. Without adequate control groups. you can't always tell whether the critical factor was. One flaw with quasi experimental designs is that the groups are Naturally Occurring. That is. they are not selected by the re,earcher, they are selected by naure. Examples of studies with this characteristic are: 'Comparing achievcment level of first-born children with that oflater-bom children. 'Comparing student performance at two schools, one of which has a lower student-teacher ratio: IQ and birth weight (of twins) At the core of the problem with these designs is how the participant, are assigned to groups. To be an experimental design, they must be assigned randomly to at least one group. This i, often difficult to do in the world outside ofa lahoratory. For example, if you're using pre-existing groups (e.g., the students in two classrooms, people whogroups (e....
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- Fall '09