handout_3_1_fall11 - 3.1 Design of Experiments experimental...

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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 Randomized Comparative Experiments “Gastric freezing” is a treatment for ulcers in the upper intestine. The patient swallows a deflated balloon with tubes attached, and 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 (uncontrolled experiment ) showed gastric freezing relieved ulcer pain. The design of the experiment was: provide 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. “How can researchers address this problem? The best solution is through the gold standard of testing for causality: randomized trials . Randomized trials involve taking a group of volunteers and randomly assigning them to either a treatment group , which gets the medical treatment, or a control group , which does not. Effectively, volunteers are assigned to treatment or control by the flip of a coin. …because of the definition of
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handout_3_1_fall11 - 3.1 Design of Experiments experimental...

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