Statistical Sciences 1023A/B Chapter 5: Chapter 5

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Statistical Sciences
Statistical Sciences 1023A/B
Lori Murray

Chapter 5 Experiments and Observational Studies Experiments and Observational Studies Explanatory and Response Variables Explanatory variable: is one that may explain or cause differences in a response variable. Response variable: is the outcome variable. Example: Study finds that overall left handed people die at a younger age than righthanded people. Experiments and Observational Studies Treatments A treatment is one or a combination of categories of the explanatory variable(s) assigned by the experimenter. Collection of conditions. Example: Salk Experiment (Chapter 1) Explanatory variable: whether or not the baby listened to a heartbeat Two treatments: heartbeat or silent Response: weight gain Experiments and Observational Studies Randomized Experiment Create differences in the explanatory variable (one that may cause differences in an outcome) and examine results (response variable). Observational Study Observe differences in the explanatory variable and notice whether these are related to differences in the response variable. Experiments and Observational Studies Two reasons why we must sometimes use an observational study instead of an experiment: 1. It is unethical or impossible to assign people to receive a specific treatment. 2. Certain explanatory variables are inherent traits and cannot be randomly assigned. Examples? Experiments and Observational Studies Confounding Variables A confounding variable is related to the explanatory variable and affects the response variable. Two variables are confounded when its hard to separate how they affect the response The effect of a confounding variable on the response variable cannot be separated from the effect of the explanatory variable on the response variable. The extra variable you didnt account for Confounding variables are a bigger problem in observational studies. Researchers try to measure possible confounding variables and see if related to the response variable. When an explanatory and response variable have been identified, confounding variables have the following traits: Differing from the explanatory variable means you differ from the confounding Differing confounding variable = differing response variable
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