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# Lec_ch4 - Chapter 4 Gathering data Learn How to gather"good...

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Agresti/Franklin Statistics, 1 of 56 Chapter 4 Gathering data Learn …. How to gather “good” data About Experiments and Observational Studies

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Agresti/Franklin Statistics, 2 of 56 Section 4.1 Should We Experiment or Should we Merely Observe?
Agresti/Franklin Statistics, 3 of 56 Population, Sample and Variables Population : all the subjects of interest Sample : subset of the population - data is collected on the sample Response variable : measures the outcome of interest Explanatory variable : the variable that explains the response variable

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Agresti/Franklin Statistics, 4 of 56 Types of Studies Experiments Observational Studies
Agresti/Franklin Statistics, 5 of 56 Experiment A researcher conducts an experiment by assigning subjects to certain experimental conditions and then observing outcomes on the response variable The experimental conditions, which correspond to assigned values of the explanatory variable, are called treatments

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Agresti/Franklin Statistics, 6 of 56 Observational Study In an observational study , the researcher observes values of the response variable and explanatory variables for the sampled subjects, without anything being done to the subjects (such as imposing a treatment)
Agresti/Franklin Statistics, 7 of 56 Example: Does Drug Testing Reduce Students’ Drug Use? Headline: “ Student Drug Testing Not Effective in Reducing Drug Use Facts about the study: 76,000 students nationwide Schools selected for the study included schools that tested for drugs and schools that did not test for drugs Each student filled out a questionnaire asking about his/her drug use

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Agresti/Franklin Statistics, 8 of 56 Example: Does Drug Testing Reduce Students’ Drug Use?
Agresti/Franklin Statistics, 9 of 56 Example: Does Drug Testing Reduce Students’ Drug Use? Conclusion: Drug use was similar in schools that tested for drugs and schools that did not test for drugs

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Agresti/Franklin Statistics, 10 of 56 Example: Does Drug Testing Reduce Students’ Drug Use? What were the response and explanatory variables?
Agresti/Franklin Statistics, 11 of 56 Example: Does Drug Testing Reduce Students’ Drug Use? Was this an observational study or an experiment?

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Agresti/Franklin Statistics, 12 of 56 Advantages of Experiments over Observational Studies We can study the effect of an explanatory variable on a response variable more accurately with an experiment than with an observational study An experiment reduces the potential for lurking variables to affect the result
Agresti/Franklin Statistics, 13 of 56 Experiments vs Observational Studies When the goal of a study is to establish cause and effect , an experiment is needed There are many situations (time constraints, ethical issues,. .) in which an experiment is not practical

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Agresti/Franklin Statistics, 14 of 56 Good Practices for Using Data Beware of anecdotal data Rely on data collected in reputable research studies
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## This note was uploaded on 04/22/2008 for the course STAT 280 taught by Professor Thomas during the Spring '08 term at Rice.

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Lec_ch4 - Chapter 4 Gathering data Learn How to gather"good...

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