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Unformatted text preview: Math 127B, Notes for lecture 6 Mrinal Raghupathi Wednesday, February 2nd, 2011 Administrivia The topics to be discussed today are the accuracy of percentages and confidence intervals. Most of the material is examples from chapter 21. Reminders 1. Read chapter 22.1, 22.2, 22.3 for Monday. There is an online quiz posted due by Monday 8 am. 2. Homework 3 is due Thursday, 2/3 in recitation. 3. There will be a quiz in recitation over chapter 20. 1 Examples from chapter 21 Example 1 . This is problem A3 in Chapter 21. In a simple random sample of 100 graduates from a certain college, 48 were earning $50,000 or more. Estimate the percentage of all graduates of that college earning $50,000 or more. Put a give-or-take number on the estimate. The percentage of graduates earning more than $50,000 in our sample is 48%. We use this number in our bootstrap estimate of the SD of the box. We have SD of the box . 48 . 52 = . 499 . 5. The SE of the sum is given by 100 . 5 = 5. The SE of percentages is 5 100 100 = 5% . The number of college graduates who earn more than $50,000 is 48% give or take 5%. o Example 2 . This is problem A5 in chapter 21. In a certain state a sample of 400 people was taken from all persons who work at manufacturing establishments. 187 people in the sample worked atfrom all persons who work at manufacturing establishments....
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