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 giveortake 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
≈
√
0
.
48
×
0
.
52 =
0
.
499
≈
0
.
5. The SE of the sum is given by
√
100
×
0
.
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 at
an establishment which had 100 employees or more. Estimate the percentage of people who worked
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '11
 Staff
 Math, Statistics, Jimmy Carter, Simple random sample, The Gallup Organization, Gallup poll, George Gallup

Click to edit the document details