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Chapter_9

# Chapter_9 - STAT 2053 Elementary Statistics Chapters 9...

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STAT 2053 – Elementary Statistics Chapters 9 – Producing Data: Experiments 1

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Chapter 9 Chapter 8 focused on proper techniques to gather data through observation and questioning. The techniques described do not influence any of the individuals in the sample; they merely observe. However, Chapter 9 discusses how to gather data through experimentation, where we introduce some treatment on the individuals and observe the response. 2
From Chapter 4 Definition : If we think a variable X explains or causes a change in another variable Y, we call X an explanatory variable , and we call Y a response variable . a response variable measures what happens to the individuals in the study an explanatory variable explains or influences changes in a response variable in an experiment , we are interested in studying the response of one variable to changes in the other (explanatory) variables. 3

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4 Explanatory and Response Variables What do you think are some reasonable explanatory variables for how well a student does on an exam?
5 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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6 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)
7 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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Experimental Design What we observe out in the real world may not be fully explained by the variable we are interested in: Example : An observational study showed that people who drink moderate amounts of alcohol have less heart disease. However, moderate drinkers also tend to have healthier habits, which may be the true cause of their healthier hearts. 8
the values for our response variable as we change the values of our explanatory variables in a controlled environment. The problem: Definition : Two variables are confounded when their effects on a response variable cannot be distinguished from one another. (In the alcohol example, drinking habits and lifestyle habits are confounded). 9

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Chapter_9 - STAT 2053 Elementary Statistics Chapters 9...

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