Lecture 12 - Comm. 88 Lecture 12 November 6, 2008 Types of...

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Comm. 88 Lecture 12 November 6, 2008 I. Types of Exp’l Designs A. Design Notation: 1. X: manipulation/treatment 2. O: Observation (measure for DV) 3. R: Random assignment B. True (Full) Experiments 1. Posttest only (control group) design a. No pre-test, just a manipulation and some type of observation. b. R X O1 (group 1) c. R O1 (group 2) i. Example: Effects of anti-smoking ad… 2. Pretest-Posttest (control group) design a. R O1 X O2 (group 1) b. R O1 O2 (group 2) c. Benefit of pretest, you can see where they stand on a certain issue. d. Possible problem: interaction of manipulation with pretest. i. Pretest can sensitize people to a certain topic. C. Solomon four-group design II. Pretesting: should you or shouldn’t you? A. Useful: 1. To “check” on RA (random assignment) 2. To get information on change. B. But: 1. Not necessary to establish causality 2. Bad idea if treatment/pretest interaction is likely III. Threats to Internal Validity A internal validity means you can be sure that X caused Y
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Lecture 12 - Comm. 88 Lecture 12 November 6, 2008 Types of...

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