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## Essential Questions

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**Friday, November 5**Essential Questions • How do I study different sampling methods for collecting data?**7.5**Select and Draw Conclusions from Samples Margin of Error Formula When a random sample of size n is taken from a large population, the margin of error is approximated by: Margin of error = Which means that if the percent of the sample responding a certain way is p (expressed as a decimal), then the percent of the population that would respond the same way is likely to be between p – ____ and p + ____.**7.5**Select and Draw Conclusions from Samples Types of Sampling Self-selected sampling: The person conducting the survey chooses the people he/she wants to participate in the survey. Systematic sampling: Involves a random start and then proceeds with the selection of every kth element from then onwards. Convenience sampling: A sample population is selected because it is readily available and convenient. Random sampling: A sampling where each member of the population has an equal and known chance of being selected.**7.5**Select and Draw Conclusions from Samples Classify samples Example 1 A student wants to survey everyone at his school about the quality of the school’s assemblies. Identify the type of sample described as a self-selected sample, a systematic sample, a convenience sample, or a random sample. • The student surveys every 8th student that enters the assembly. Solution • The student uses a rule to select students, so the sample is a ____________ sample.**7.5**Select and Draw Conclusions from Samples Classify samples Example 1 A student wants to survey everyone at his school about the quality of the school’s assemblies. Identify the type of sample described as a self-selected sample, a systematic sample, a convenience sample, or a random sample. • From a random lottery, the student chooses 125 students and teachers to survey. Solution • The student chooses from a random name lottery, so the sample is a __________ sample.**7.5**Select and Draw Conclusions from Samples Checkpoint. Identify the type of sample described. • A local mayor wants to survey local area registered voters. She mails surveys to the individuals that are members of her political party and uses only the surveys that are returned. She selected the ones that she wanted to survey.**7.5**Select and Draw Conclusions from Samples Identify biased solutions Example 2 Tell whether each sample in Example 1 is biased or unbiased. Explain your reasoning. • The student surveys every 8th student that enters the assembly. Solution • The sample is ____________ because the student surveys the students, but not the teachers.**7.5**Select and Draw Conclusions from Samples Identify biased solutions Example 2 Tell whether each sample in Example 1 is biased or unbiased. Explain your reasoning. • From a random lottery, the student chooses 125 students and teachers to survey. Solution • The sample is ____________ because both students and teachers are surveyed.**7.5**Select and Draw Conclusions from Samples Checkpoint. Complete the following exercises. • Tell whether the sample in Exercise 1 is biased or unbiased. Explain your reasoning. Because the survey is mailed to only those who are members of one political party.**7.5**Select and Draw Conclusions from Samples Find a margin of error Example 3 Newspaper Survey In a survey of 325 students and teachers, 30% said they read the school’s newspaper every weekday. • What is the margin of error for the survey? Solution • Margin of error = The margin of error for the survey is about ______%.**7.5**Select and Draw Conclusions from Samples Find a margin of error Example 3 Newspaper Survey In a survey of 325 students and teachers, 30% said they read the school’s newspaper every weekday. • Give an interval that is likely to contain the exact percent of all students and teachers who read the school newspaper every weekday. Solution • To find the interval, add or subtract _____%. It is likely that the exact percent of all students and teachers who read the school’s newspaper every weekday is between _____% and _____%.**7.5**Select and Draw Conclusions from Samples Checkpoint. Complete the following exercises. • In Example 3, suppose the sample size is 400 students and teachers. What is the margin of error for the survey?**7.5**Select and Draw Conclusions from Samples Pg. 282, 7.5 #1-20