Chapter 12 Section 5 Working With Samples Algebra

Chapter 12 Section 5 Working With Samples Algebra 2 ~ February 18, 2009

Warm-Ups Determine the whole number of standard deviations that includes all data values: The mean length of Beethoven’s nine symphonies is 37 minutes; the standard deviation is 12 minutes 27 min, 30 min, 47 min, 35 min, 30 min, 40 min, 35 min, 22 min, 65 min

Standard Deviation on the Calculator Find the mean and the standard deviation of the following values using your graphing calculator: 1. ) 78 90 456 673 111 381 21 2. ) 13 15 17 18 21 21 10

Sample Proportions � Sample: gathers information from only part of a population � Sample Proportion = �x is the number of times an event occurs � n is the sample size � Example: In a sample of 350 teenagers, 294 have never made a snow sculpture. Find the sample proportion for those who have never made a snow sculpture.

Sample Proportions �Two major factors that influence the reliability of samples: 1. Sampling Bias 2. Sample Sizes

What is “Bias”? ?

Bias in Sampling Bias: To show favoritism in a person or thing; to influence unfairly; prejudice A news program reports on a proposed school dress code. The purpose of the program is to find what percent of the population in its viewing area favors the dress code. Discuss the bias in the three types of sampling methods. Viewers are invited to call in and express their preferences A reporter interviews people on the street near the local high school During the program, 300 people are selected at random from the viewing area. Then each person is contacted.

Bias in Sampling The Sunnyvale High School student council dance committee is trying to decide whether to have a band or a DJ for the fall dance. They decided that each of the four committee members should survey the students in their homeroom classes. Identify any bias in this sampling method.

Comparing Sampling Sizes How would the size of the sample affect the results? ?

Using the Margin of Error � The larger the sample size, the smaller the margin of error � Example: A survey of 2580 students found that 9% are left-handed. � Find � Use the margin of error for the sample the margin of error to find the interval that is likely to contain the population proportion

Using the Margin of Error Example 2: A recent poll reported that 56% of voters favored President Obama’s Stimulus Plan, with a margin of error of. Estimate the number of participants in the poll. Use the margin of error to determine the likely range for the true population proportion

Homework #26 Pg 680 #1, 2, 4, 5, 8 -10, 12, 13, 16, 18, 20, 32