Chapter_09 - Chapter 9 Producing Data: Experiments BPS -...

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BPS - 5th Ed. Chapter 9 1 Chapter 9 Producing Data: Experiments
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BPS - 5th Ed. Chapter 9 2 How Data are Obtained Observational Study Observes individuals and measures variables of interest but does not attempt to influence the responses Describes some group or situation Sample surveys are observational studies Experiment Deliberately imposes some treatment on individuals in order to observe their responses Studies whether the treatment causes change in the response.
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BPS - 5th Ed. Chapter 9 3 Experiment versus Observational Study Both typically have the goal of detecting a relationship between the explanatory and response variables. Experiment create differences in the explanatory variable and examine any resulting changes in the response variable ( cause-and-effect conclusion) Observational Study observe differences in the explanatory variable and notice any related differences in the response variable ( association between variables)
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BPS - 5th Ed. Chapter 9 4 Why Not Always Use an Experiment? Sometimes it is unethical or impossible to assign people to receive a specific treatment. Certain explanatory variables, such as handedness or gender, are inherent traits and cannot be randomly assigned.
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BPS - 5th Ed. Chapter 9 5 Confounding The problem: in addition to the explanatory variable of interest, there may be other variables (explanatory or lurking ) that make the groups being studied different from each other the impact of these variables cannot be separated from the impact of the explanatory variable on the response
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BPS - 5th Ed. Chapter 9 6 Confounding The solution: Experiment : randomize experimental units to receive different treatments (possible confounding variables should “even out” across groups) Observational Study : measure potential confounding variables and determine if they have an impact on the response (may then adjust for these variables in the statistical analysis)
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BPS - 5th Ed. Chapter 9 7 Question A recent newspaper article concluded that smoking marijuana at least three times a week resulted in lower grades in college. How do you think the researchers came to this conclusion? Do you believe it? Is there a more reasonable conclusion?
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BPS - 5th Ed. Chapter 9 8 Case Study The Effect of Hypnosis on the Immune System reported in Science News , Sept. 4, 1993, p. 153
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BPS - 5th Ed. Chapter 9 9 Case Study The Effect of Hypnosis on the Immune System Objective: To determine if hypnosis strengthens the disease-fighting capacity of immune cells.
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BPS - 5th Ed. Chapter 9 10 Case Study 65 college students 33 easily hypnotized 32 not easily hypnotized white blood cell counts measured all students viewed a brief video about the immune system
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BPS - 5th Ed. Chapter 9
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Chapter_09 - Chapter 9 Producing Data: Experiments BPS -...

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