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Please get out materials for notes. Make sure to grab a outline at the front desk.

Please get out materials for notes. Make sure to grab a outline at the front desk. The Current Event Project will be due on Tuesday, September 13 th. Ch. 4: Designing Studies. Section 4.1 – Samples & Surveys. Samples and Surveys. IDENTIFY the population and sample in a statistical study.

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Please get out materials for notes. Make sure to grab a outline at the front desk.

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  1. Please get out materials for notes. • Make sure to grab a outline at the front desk.

  2. The Current Event Project will be due on Tuesday, September 13th.

  3. Ch. 4: Designing Studies Section 4.1 – Samples & Surveys

  4. Samples and Surveys • IDENTIFY the population and sample in a statistical study. • IDENTIFY voluntary response samples and convenience samples. EXPLAIN how these sampling methods can lead to bias. • DESCRIBE how to obtain a random sample using slips of paper, technology, or a table of random digits. • DISTINGUISH a simple random sample from a stratified random sample or cluster sample. Give the advantages and disadvantages of each sampling method. • EXPLAIN how undercoverage, nonresponse, question wording, and other aspects of a sample survey can lead to bias.

  5. Population, Census, and Sample Population - a statistical study is the entire group of individuals we want information about. Census - collects data from every individual in the population. Sample - a subset of individuals in the population from which we actually collect data. Population Collect data from a representative Sample... Sample Make an Inference about the Population.

  6. Example on P. 210 • Identify the population and the sample in each of the following settings: a) A furniture maker buys hardwood in large batches. The supplier is supposed to dry the wood before shipping (wood that isn’t dry won’t hold its size and shape). The furniture maker chooses five pieces of wood from each batch and tests their moisture content. If any piece exceeds 12% moisture content, the entire batch is sent back. b) Each week, the Gallup Poll questions a sample of about 1500 adult U.S. residents to determine national opinion on a wide variety of issues.

  7. The Idea of a Sample Survey Choosing a Sample Step 1: Define the population we want to describe. Step 2: Say exactly what we want to measure. Sample survey- a study that uses an organized plan to choose a sample that represents some specific population. Step 3: Decide how to choose a sample from the population.

  8. How to Sample Badly How can we choose a sample that we can trust to represent the population? Choosing individuals from the population who are easy to reach results in a convenience sample. Convenience samples often produce unrepresentative data…why? The design of a statistical study shows bias if it would consistently underestimate or consistently overestimate the value you want to know.

  9. How to Sample Badly A voluntary response sample consists of people who choose themselves by responding to a general invitation. Voluntary response samples show bias because people with strong opinions (often in the same direction) are most likely to respond.

  10. AP Exam Tip, P. 212 If you’re asked to describe how the design of a study leads to bias, you’re expected to do the following: • Identify a problem with the design. • Explain how this problem would lead to an underestimate or overestimate.

  11. Check Your Understanding P. 213 • For each of the following situations, identify the sampling method used. Then explain how the sampling method could lead to bias. • A farmer brings a juice company several crates of oranges each week. A company inspector looks at 10 oranges from the top of each crate before deciding whether to buy all the oranges. • Convenience sampling – This could lead to the inspector overestimating the quality of the oranges if the farmer puts the best oranges on top.

  12. Check Your Understanding P. 213 • For each of the following situations, identify the sampling method used. Then explain how the sampling method could lead to bias. • The ABC program Nightline once asked whether the United Nations should continue to have its headquarters in the U.S.. Viewers were invited to call one telephone number to respond “Yes” and another for “No.” There was a charge for calling either number. More than 186,000 callers responded, and 67% said “No.” • Voluntary response sampling – those who are happy that the UN has its headquarters in the U.S. already have what they want and so are less likely to respond. The proportion who answered “No” in the sample is likely to be higher than the true proportion in the U.S. who would answer “No.”

  13. How to Sample Well: Simple Random Sampling A sample chosen by chance rules out both favoritism by the sampler and self-selection by respondents. Random sampling involves using a chance process to determine which members of a population are included in the sample. A simple random sample (SRS) of size nis chosen in such a way that every group of n individuals in the population has an equal chance to be selected as the sample. In practice, people use random numbers generated by a computer or calculator to choose samples. If you don’t have technology handy, you can use a table of random digits (Table D in book).

  14. Homework – Due Tuesday P. 229 – # 1 – 9 odd

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