TAMU ATMO 606 - Chapter 8 (10 pages)

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Chapter 8



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Chapter 8

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Pages:
10
School:
Texas A&M University
Course:
Atmo 606 - Atmos Chemistry I

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STAT 302 Chapter 8 Chapter 8 Designing Experiments To call in the statistician after the experiment is done may be no more than asking him to perform a post mortem examination he may be able to say what the experiment died of Ronald Fisher 1938 Review In an experiment the experimenter assigns values of the explanatory variable to each individual In an observational study experimenters observe without imposing treatments A treatment is a level of the explanatory variable randomly assigned to an individual Example Researchers studying Alzheimer s disease have been searching for genetic causes In a recent study involving Alzheimer s patients over 65 year old researchers found that patients with Alzheimer s disease had lower levels of SORL1 protein in their blood due to their having a particular variant of the SORL1 gene They found that having lower levels of SORL1 protein in the blood was statistically significantly associated with an increase in the production of the toxic A beta peptide involved in the build up of amyloid plaques in the brain Was this an experiment or observational study Example A researcher wanted to know Are adult women who take an aspirin every other day less likely to get a heart attack than adult women who do not take an aspirin every other day To answer this question a random sample of 20 000 female nurses is selected from the registry of all registered nurses Each nurse is asked if she takes an aspirin every other day or not The nurses are then followed for 5 years to determine their heart health status Was this an experiment or an observational study 125 What were the explanatory and response variables STAT 302 Chapter 8 What were the treatments Experimental units are the individuals or groups assigned to the treatments Example How do salinity and temperature affect the growth of shrimp One researcher randomly assigned two aquariums each to three different salinity levels low salt medium salt and high salt For each salinity one tank was assigned to a high temperature and one to a low temperature Then 100 shrimp were grown in each tank What were the explanatory and response variables What were the treatments What were the experimental units Key components to experimental designs 1 A control group is a treatment group used to compare to the treatment of interest Often the control group is assigned to take a medication a medication that is designed to look like the medication of interest but that has no actual effect on the body When placebos are unethical the group assigned to the standard treatment is the control group Example Gastric freezing was once a clever treatment for ulcers In one study patients swallowed a deflated balloon attached to tubes Then a refrigerated liquid was used to fill the balloon with the idea that cooling the ulcer would relieve pain 70 of patients experienced continued pain relief after experiencing this treatment What was the treatment in this study What were the



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