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handout_3_1 - 3.1 Design of Experiments experimental units...

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3.1 Design of Experiments experimental units - individuals on which the experiment is done subjects - experimental subjects that are humans treatment - specific experimental condition applied to the units factors - explanatory variables in experiment levels - specific values of the factors EX- Do smaller classes improve student performance? Tennessee STAR experiment •subjects- 6385 students •treatments- regular class (22-25) with one teacher regular class with one teacher and one full-time teacher’s aide small class (13-17) •factor- type of class result- in later years, the student from the smaller classes had higher test scores experiment- can control for lurking variables students were randomly assigned to different classes- no systematic differences between groups so differences in outcomes are attributable to differences in treatment EX- What are the effects of exposure to ads? Figure 3.2 All subjects viewed a 40-minute TV program that included ads for a digital camera. Some subjects saw a 30-second commercial; others, a 90-second version. The same commercial was show either 1, 3, or 5 times during the program •subjects- undergraduate students •2 factors- length of commercial (2 levels) and repetitions (3 levels) •6 treatments response variables- students’ attitudes toward camera…
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Comparative Experiments EX- “Gastric freezing” is a treatment for ulcers in the upper intestine. The patient swallows a deflated balloon with tubes attached, then a refrigerated liquid is pumped through the balloon for an hour: The idea is that cooling the stomach will reduce its production of acid and so relieve ulcers. The first experiment showed gastric freezing relieved ulcer pain. The design of the experiment was: gastric freezing → observe pain relief This experiment was poorly designed. The patients’ response may have been due to the placebo effect . A placebo is a dummy treatment. Many patients respond favorably to any treatment, even a placebo. This may be due to trust in the doctor and expectations of a cure or simply to the fact that medical conditions often improve without treatment. The response to a dummy treatment is the placebo effect.
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