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10/02/2007Stat245 Recitation1 Highlights in HW1 Numerical attributes (Discrete or Continuous?)  Number of students in a class of 35 who turn in a term.

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Presentation on theme: "10/02/2007Stat245 Recitation1 Highlights in HW1 Numerical attributes (Discrete or Continuous?)  Number of students in a class of 35 who turn in a term."— Presentation transcript:

1 10/02/2007Stat245 Recitation1 Highlights in HW1 Numerical attributes (Discrete or Continuous?)  Number of students in a class of 35 who turn in a term paper before the due date. (numerical: discrete)  The number of insufficient-funds checks received by a grocery store during a given month. (numerical: discrete)

2 10/02/2007Stat245 Recitation2  The number of New York Yankees during a given year who will not play for the Yankees the next year. (numerical: discrete)  The number of students in a class of 35 who have purchased a used copy of the textbook. (numerical: discrete)  Amount of fluid (in ounces) dispensed by a machine used to fill bottles with soda pop. (numerical: continuous)

3 10/02/2007Stat245 Recitation3  The amount by which a 1-lb package of ground beef decreases in weight (because of moisture loss) before purchase. (numerical: continuous)  Amount of fluid (in ounces) dispensed by a machine used to fill bottles with soda pop. (numerical: continuous)  Thickness of the gelatin coating of a vitamin E capsule. (numerical: continuous)

4 10/02/2007Stat245 Recitation4 Exercise in Chapter A petition with 500 signatures is submitted to a university’s student council. The council president would like to determine the proportion of those who signed the petition who are actually registered students at the university. There is not enough time to check all 500 names with the registrar, so the council president decides to select a simple random sample of 30 signatures. Describe how this might be done.

5 10/02/2007Stat245 Recitation A pollster for the Public Policy institute of California explains how the Institute selects a sample of California adults:  That is done by using computer-generated random residential telephone numbers with all California prefixes, and when there are no answers, calling back repeatedly to the original numbers selected to avoid a bias against hard-to-reach people. Once a call is completed, a second random selection is made by asking for the adult in the household who had the most recent birthday. It is as important to randomize who you speak to in the household as it is to randomize the household you select. If you didn’t, you’d primarily get women and older people.  Comment on this approach to selecting a sample. How does the sampling procedure attempt to minimize certain type of bias? Are there source of bias that might still be a concern?

6 10/02/2007Stat245 Recitation6 Types of Bias Selection bias  Tendency for samples to differ from the corresponding population as a result of systematic exclusion of some part of the population Measurement or response bias  Tendency for samples to differ from the corresponding population because the method of observation tends to produce values that differ from the true value. Nonresponse bias  Tendency for samples to differ from the corresponding population because data are not obtained from all individuals selected from inclusion in the sample.

7 10/02/2007Stat245 Recitation A newspaper headline stated that at a recent budget workshop, nearly three dozen people supported a sales tax increase to help deal with the city’s financial deficit. This conclusion was based on data from a survey acknowledged to be unscientific, in which 34 out of the 43 people who chose to attend the budget workshop recommended raising the sales tax. Briefly discuss why the survey was described as “unscientific” and how this might limit the conclusions that can be drawn from the survey data.

8 10/02/2007Stat245 Recitation “More than half of California’s doctors say they are so frustrated with managed care they will quit, retire early, or leave the state within three years.” This conclusion from an article titled “Doctors Feeling Pessimistic, Study Finds” (San Luis ObispoTribune, July 15, 2001) was based on a mail survey conducted by the California Medical Association. Survey were mailed to 19,000 California doctors, and 2000 completed surveys were returned. Describe any concerns you have regarding the conclusion drawn.


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