Lesson1hw1 - 1 Lesson 1 1.1 Introduction Unit summary Why...

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Lesson 1 1.1 Introduction Unit summary: Why study statistics What do statisticians do How to collect data for surveys Observational studies versus scientific studies Reading assignment : Ch 1, Ch 2 An overview of Statistics: Why study statistics? a. To evaluate printed numerical facts. b. To interpret the results of sampling or to perform statistical analysis in your work. c. To make inference about the population using information collected from the sample. 1
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e.g. A Reader’s digest/Gallup survey on the drinking habits of Americans estimated the percentage of adults across the country who drink beer, wine, or hard liquor, at least occasionally. Due to various constraints, for example, time or budget, one can only sample from the population instead of take a census of the population. We need a sample that closely represents the population. One way is to obtain a random sample. What do Statisticians do? a. gathering data b. summarizing data c. analyzing data d. drawing conclusions and reporting the results of their analyses e.g. You want to know the average amount of time American people spend browsing the web. How are you going to perform the above four steps? 2
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One Answer will be: Gathering data Why gather data? Systematic reflections on previous experience can help with many problems. In statistics, data can be gathered by a survey or a scientific study. Usually, surveys are passive where the aim is to gather data on existing conditions, attitudes, or behaviors. 3
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How to collect data for surveys The following are a few frequently used methods: 1. Personal interview People usually respond when interviewed by a person but their answers may be influenced by the interviewer. 2. Telephone interview Cost effective but need to keep it short since respondents tend to be impatient. 3. Self-administered questionnaires Cost effective but the response rate is lower and the respondents may be a biased sample. 4. Direct observation For certain quantities of interest, one may be able to measure it from the sample. 5.Web-based survey … etc. 4
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Observational studies versus scientific studies It is very important to distinguish these two types of studies since one has to be very skeptical about drawing cause and effect conclusion using observational studies: 1. Observational studies Researcher just observes the data and has no control over which subject uses what type of treatment. e.g. Survey and census 2. Scientific studies (designed experiment) Researcher impose treatments and controls and then observe characteristic and take measurements. Example : We want to decide whether Advil or Tylenol is more effective in reducing fever. Method 1: Let the subject choose Advil or Tylenol and then measure the effectiveness.
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