Chapter 6 (1) - Chapter 6 Experiments In The Real World...

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Chapter 6 Experiments In The Real World
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Outline Equal Treatment For All Double Blind Experiments Refusals, Non-adherers, And Dropouts Can We Generalize Experimental Designs in the real world Matched Pairs vs. Blocked Designs
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Randomized Comparative Experiments “Gold Standard” If possible, a study should be a randomized comparative experiment Examples Is a new medication better? Does a new fertilizer produce higher crop yields than the old fertilizer?
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Equal Treatment For All
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Randomization Recall: Randomizing group assignment ensures that the treatment group does not have an unfair advantage over the control group due to method of assignment. Unfair advantages (bias) can come from all angles Researcher needs to be able to think of all these angles BEFORE running the experiment
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Example Does a new breakfast cereal provide good nutrition? 25 rats were randomly assigned to the treatment group where they were given the new cereal and 25 rats were randomly assigned to the control group where they received the competing cereal. The treatment group gained more weight than the control group. Can you think of possible bias sources? How were the rats fed? When? Where were they “stored”?
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Example cont. After, further inspection we notice that each group of rats was placed in a different cage. It turns out that the cage of rats who received the cereal were placed next to a radiator. Knowing this, is the experiment still valid? Did all the rats receive equal treatment (accept for diet)?
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Example 20 patients were randomly divided into two groups. One group (the treatment group) received an eye drop that was thought to relieve redness while the other group (the control group) received regular water drops. A doctor evaluated each patient’s redness and scored them on a scale of 1-10 with 10 being the most red. The treatment group was statistically significantly less red. If the doctor knew who got the treatment, which may explain why the treatment group differed from the control group in the end? A. The doctors new who should receive relief and so unintentionally biased results B. The treatment worked C. Both A and B D. Neither A and B Suppose that the patients evaluated eye redness themselves in a mirror thus eliminating any unfair advantage that might be gained from the doctor’s knowledge of the experiment. Do you think that you (the subject) could tell the difference between regular water in your eye and an eye drop designed to soothe discomfort?
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Placebos
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Chapter 6 (1) - Chapter 6 Experiments In The Real World...

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